David Owen says Theresa May “has been badly advised and seems unaware” of “a complete error of a very serious kind”, as Number Ten tries to pretend we are not staying in the European Economic Area during her Brexit plan.

Owen releases recent letters between himself and the Prime Minister which in his view demonstrate “that the machinery around her can make an elementary mistake” and is “pushing out disinformation”.

He laments that the Government contains “not one single person in a senior position who’s had long experience of negotiating with the EU. Not one! Not one! They have a team of people who are inexperienced on EU negotiations, and some of them have never before done anything in this area.”

In the early 1970s Owen was one of the Labour rebels who voted with Edward Heath to take Britain into the Common Market, from 1977-79 he served as Foreign Secretary, in the early 1980s he belonged to the “Gang of Four” who left Labour and founded the SDP, and in 2016 he campaigned for Vote Leave in the EU Referendum. He has written numerous books, including Hubris – The Road to Donald Trump, which will be published by Methuen on 1st November. In the interests of full disclosure I should add that I am his godson.

The editor of ConHome commissioned this interview in order to establish how the former Foreign Secretary thinks the Prime Minister should approach the final Brexit negotiations.

Owen dismisses as “vainglorious” the idea of leaving the EU without a deal, observes that there would be no Commons majority for doing so, and begins by outlining the changes which he is urging May to make in order to achieve a Canada plus plus plus deal, including “no full payment of the £38 billion” until a timetable for such a deal has been agreed.

ConHome: “You’re well known for pushing this idea of joining the EEA and then moving to Canada plus – is it too late for that? After all, negotiating anything takes time.”

Owen: “A staged Brexit should be built into the Withdrawal Agreement, which is a very substantial document already, and deals with almost all the immediate issues that we would otherwise face coming out without an agreement.

“And part of that agreement has a 21-month pause in which in the words of the footnote to Article 124 of the Withdrawal Agreement reads the UK is considered still to be a member of the EU. And yet this ‘vassal state’ deal as described by Jacob Rees-Mogg has been accepted by most hard-line Brexiteers.

“And it means that for 21 months we are almost in what you might call purdah. We are technically assumed to be still members of the EU, although we are not, but we are given a very good standstill period which goes beyond EEA, it deals with banks and it deals with almost everything.

“So I think we should keep to the Withdrawal Agreement, we should negotiate everything we can within the framework of the Withdrawal Agreement, and we should try to, in the Withdrawal Agreement, timetable everything on the basis of achieving Canada plus plus plus.

“Which is Tusk’s wording, not our wording now. Tusk has said he offers a Canada plus plus plus – three plusses.

“In those three plusses you would hope to take some elements of the agreed 21-month standstill. Hopefully I would argue that we should drop vassal status and be a full member of the EFTA pillar of governance of the EEA as soon as that 21-month period starts.

“The EU may refuse. Why did they put us in this purdah period with no voice or vote? Probably, to be blunt, they didn’t trust us. They thought we would use formal membership as a non-EU member of the EEA to block some of their regulations.

“But I’m a pragmatist. This has been accepted by the Conservative MPs, accepted by Boris, accepted by David Davis. So I’d accept settling for that, leave it.

“But when that 21-month period elapses, in no way will you have got near to a Canada plus plus plus free trade agreement. What are we going to do? Just carry on in this semi-purdah?

“And the answer is nobody’s filled this in. So we must fill it in. We must know what’s going to happen. It is in our interests to extend this standstill period until we have a Canada plus plus plus agreement. Yet during this period from 21 months we must become a full non-EU member of the EEA with the other three. And assume their full rights.

“One of the things that would then happen during that period is that we would be able to start our independent fishing policy, which is important in dealing with the pressures we’re coming under in Scotland and in the fishing areas. And we would be able to start on our agricultural policy.

“But apart from these two areas, the rest of the standstill period would hold. But we’d cease to be a vassal state, and we’d be heading where we want to be, which is out.

“Then we would have to write in to the Withdrawal Agreement that there would be no full payment of the £38 billion until we had reached an agreement on Canada plus plus plus. That should ideally be in 2022. Three years until an FTA is in place is on the optimistic side but it is realistic as we are already party to the EU-Canada Agreement and we start negotiating with the EU from a common position.

“So I do not accept – and nor should the UK Government – that Canada plus plus will take eight, ten years, six years, and I think it’s a farce to contemplate such a timescale. When you tell your negotiators to reach an agreement in a specified timescale, they do so.

“So the negotiations from the end of the 21-month period on 31st December 2020 will be how much we can keep of the standstill period and how much we can’t keep. It’s a practical matter and we know it cannot be Chequers.

“We would have given the one year’s notice on 31st March 2021 as a member of the non-EU EEA, a contracting party to the Agreement which we signed ourselves as UK, so we would be out by the next election, which has to take place by June 2022. That gives a three-year period from when we left the EU to negotiate and agree and ratify a Canada deal.

“To those critics of a three-year period and who say we may need four we will know if there is good will during the negotiations and are making good progress in which case a government might decide that they have to accept as the absolute deadline giving notice to leave before the election but allowing some months more in 2022.

“The great advantage that we have as a non-EU contracting party to the EEA is it is the British Government that chooses its own exit time. It is an interesting fact that the British Government has not yet given one year’s notice of leaving the EEA and we are technically in breach of the Agreement.

“I now get to the politics, OK? I have a pack of letters which I will give you. I’ve been writing correspondence to the Prime Minister. And I started in 2016. They are on my website.

“This is a courteous exchange. I never automatically assumed that the Prime Minister would reply to me. She could have shunted it off to a junior minister. She didn’t, and I’m grateful to her. I always had only one issue with her. If your bespoke agreement runs into difficulties and you can’t deliver it, then you must have as a backstop EEA membership.

“It is not realistic, and you will not get it through the House of Commons, if you try to go out with no deal. This is vainglorious stuff.

“And she rightly understood early on that we needed a transition period. But she has come under some very bad advice in trying to pretend all through her bespoke period that we were not part of the EEA. I assume this is because the hard Brexiteers don’t like being in the EEA because they fear you’d be there permanently. So they and the Government have been consistently misrepresenting the EEA.

“In the Prime Minister’s letter to me on the 6th September 2018, she says in the third to last paragraph:

“I should also add that the EEA would not provide a solution for the Irish border issue. It would deal with industrial goods, but not checks on sanitary and phytosanitary standards for agrifood, nor with customs.”

“That is a complete error of a very serious kind, frankly.

“Now what that shows – and we all know the Prime Minister can’t always read every letter – is that the machinery around her can make an elementary mistake. The very first Annex to the EEA Agreement, and I quote here my own letter [of 17th September 2018] to her,

“is devoted to these issues of sanitary and phytosanitary standards for agrifood. The Annex is for the most part a 269-page bibliography of the relevant legislative Acts concerning SPS matters which are contained in the EEA acquis.”

“Now it gets worse than that. The Government has been pushing out disinformation concerning the EEA over the last few weeks. They have created a post on Facebook which is ostensibly to provide public information. The video contains a number of assertions about the EEA, each presented as factual, but each false.

“The most egregious false assertion is that the EEA entails membership of the EU customs union, which it does not, and that it would therefore prevent the UK from striking its own free-trade agreements with other countries. It would not, and it’s only necessary to look at the Norwegian list of free-trade agreements.

“So on top of the error in her letter to me, they’re now adopting these tactics. This video [voiced by Theresa May and posted on her Facebook page on 17th September] makes the assertion that EEA membership entails the payment of ‘vast’ sums of money to the EU.

“If we were to become a non-EU member of the EEA now, the minimum and the maximum we have to pay is about £1.5 billion a year. This is in comparison to a government that is paying out £38 billion in the Withdrawal Agreement anyhow.

“So we can’t carry on a rational argument on membership of the EEA because they don’t want to admit that in the Withdrawal Agreement they’ve already written, we are members of the EEA. If under the footnote to Article 124 ‘the United Kingdom is to be treated as a Member State for the purposes of these agreements’, that puts us in the EU pillar of the EEA.

“They cannot go on avoiding admitting that we will be part of the EEA while we negotiate Canada plus plus plus. You can’t be a a vassal state member of the EU without being in the EEA.”

ConHome: “So we’re already in the EEA.”

Owen: “We’re already in the EEA.”

ConHome: “It’s like the play by Molière where the man says he has been speaking prose without knowing it.”

Owen: “We are in the EEA now and under the 21-month pause period we’re in the EEA, and during that period we’re dealing with agriculture in Northern Ireland and all these different tests under EEA powers.

“Now there is a provision for a country like us who’ve left the EU to be a non-EU member of it, and with it comes rights.”

ConHome: “By the way, are Norway and the other EEA members happy for us to do that, even though they know we’re proposing to leave the EEA club later on?”

Owen: “Yes. Exactly. The only thing is to get it through the House of Commons with all the animosity over any membership of the EEA from some people.”

ConHome: “Could you specify who ‘some people’ are?”

Owen: “Well Rees-Mogg, I am not certain about Boris and David Davis.”

ConHome: “Have you spoken to them? Have you tried to convince them of the error of their ways?”

Owen: “Well what you have to remember is that during the referendum there was never any discussion about how we were going out. But there were a very large number of us who were Brexiteers who thought we would come out in some way through the EEA mechanism, because it’s a soft way of gradually moving out.”

ConHome: “I think officially, am I right in remembering, that David Cameron was against it, and so were the hard-line Leavers?”

Owen: “Yes. I’m totally against staying in the EEA permanently, I’ve never believed that that’s the place for us, and I wished her well on her bespoke agreement, I didn’t even argue against that if she could get it all out, good – but now I think she faces a problem, which is what to do after 21 months. Are we going to continue in that state?

“And so I have not yet seen any wording on how they intend to bridge the gap between the end of the 21-month period and getting a Canada plus plus plus. And the obvious way to deal with it is to be within the non-EU part of the EEA.

“And you would win some friends on this. But the trouble is there are some people who advocate the EEA with the intention of locking us in, permanently. And I think the way to deal with this is the Withdrawal Agreement specifies forward commitments.

“So when we ask, as we have to, EFTA to allow us to come in, we tell them, we’ll come in and we’re coming for a period and we will give in our notice in the lifetime of this Government. And I think that’s reasonable and as far as I could go…

“I think there are many people in the EU who can’t wait for the damn thing to be settled.

“I have actually spent quite a lot of my time making international negotiations and treaties, and one of the ways when you run into difficulty is that you stagger the process. You timetable it and you go through different phases.

“I think three years is realistic. And you give an incentive to the EU, part of the big money, and you then pay your dues to the EU during this extra 15-month period. The whole process would take three years and during that period we would solve the Irish problem. How can you not do so? Trust would develop, and the whole thing as we know is highly political.

“We are in the EEA now, we are going to be in it for the 21 months, and it would make a reasonable pathway for the further 15 months, and we’re out of it all before a June 2022 general election.

“If the pessimists are right and it will take four years we will know that at the start of 2022 and if the Government really felt confident we could extend beyond the election but only if we give notice on 31st March 2022 that we are exiting completely.

“That way at the election the people will know the die has been cast and we are finally exiting by a known date.”

ConHome: “Why is the Prime Minister not receptive to this argument?”

Owen: “I think she had to accommodate David Davis’s view – he has always feared the EEA would end up being the permanent position. That is why we have to specify a timetable within the Withdrawal Agreement when we will definitely be out of the EU and the EEA.

“If the EU were to refuse a transition out through the EEA, I still believe we can use the Vienna Convention and its arbitration procedures and assert our right to be a continuing member of the EEA and the EFTA governance. It’s very disobliging to have to do that but I don’t think we’re totally powerless. And I would certainly argue that if they reach no agreement by say 15th December, we will assert our right to be a continuing member of the EEA, and I doubt we would need to go to the court.

“Another reason is that the ECJ is a regional court. And that means they can be overridden by the Vienna Convention. They won’t like that…

“Also we can dock alongside the EFTA Court, as the EU suggested for Switzerland, and thereby escape any involvement of the ECJ. The EU have always been clear that any Agreement has to have a court procedure. They accept the EFTA Court.

“The problem with the Government and the problem with their position is there’s not one single person who’s had long experience of negotiating with the EU. Not one! Not one! They have a team of people who are inexperienced on EU negotiations, and some of them have never before done anything in this area.”

ConHome: “Do we need a new Prime Minister to do this?”

Owen: “No. It’s none of my business anyhow. I’m not a member of the Tory Party. I’ve not got into that argument. At this stage in the game, what we do need is a great deal more cross-party unity on it all.”

ConHome: “Some readers will remember that with Roy Jenkins you voted to help get us into the Common Market in 1971. When did you change your mind?”

Owen: “I formally changed my mind when Cameron came back with nothing, I thought, of substance. I didn’t finally make up my mind until then, but I had been moving in that direction.

“In 1999 I became chairman of a thing called New Europe. It was an all-party group, Nigel Lawson was very active in it and so was Denis Healey, and we had one aim, which was to stop Tony Blair winning a referendum on Euro entry on what was called in Number Ten the back of the Baghdad bounce.”

ConHome: “We’re on to hubris now, I think.”

Owen: “I’m a totally enthusiastic European but I’m absolutely against federalism. And I think the single currency was a federalist move, and the [British] opt-out didn’t help, actually. The pressure was building up on us all the time to enter the Eurozone. Then when it failed and we saw countries like Greece utterly screwed, then I realised how undemocratic it was.

“I consider Macron now is the first real head of state of a big country to be an absolutely outright supporter of a federal Europe.”

ConHome: “The Germans are going to disappoint Macron, aren’t they?”

Owen: “Who knows? The Monnet thesis is that out of crisis comes progress. There’s going to be a crisis with the Italian economy. Now they will not bail out Italy, but they would be prepared, Germany, properly handled, in a crisis, to agree to a tight Eurozone with fiscal transfers, but it would be a small grouping of six or seven.

“Eventually I believe there will be a federal union involving France and Germany. They’ll hang Italy out to dry just like they did the Greeks. It’ll be France, Germany, Belgium, Holland, Luxembourg, and I think that would probably be it. Spain would like to be in it. They might, but I don’t think so.”