Stephen Booth is Acting Director of Open Europe.

If we get there, phase two of the Brexit negotiations will be constrained by political dynamics in the UK and the EU, which are being driven by the choices made by both sides to date. The sum of all the moving parts now points to a choice between a relatively straightforward trade agreement or a WTO-terms exit at the end of the transition. Given the circumstances, there is some logic to condensing the negotiating period, keeping things simple and leaving open the option of deeper political and economic cooperation once the dust has settled.

Previously, I have noted that, if Boris Johnson is successful in the coming election, ratifying the Withdrawal Agreement only brings the first phase of Brexit to a conclusion. To recap, the WA provides a “transition period” that is due to end on 31st December 2020. There will still be much left to do in this period, including settling a successor UK-EU trade relationship.

The Conservatives’ definitive manifesto pledge not to extend the transition raises the stakes by only providing around 11 months to conclude a UK-EU trade negotiation. Whether a resulting trade agreement could also be ratified and implemented by government and businesses within that timeframe is likely to be another matter. But an implementation period would be distinct from an extension in order to continue negotiating.

Firstly, it is obvious why a transition extension would be controversial on the UK side of the table. “Get Brexit done” is the rallying cry of the Conservative campaign, and the pledge to rule out an extension is at least partly responsible for Nigel Farage’s decision to call off the Brexit Party campaign in Tory-held seats.

Extending would not be a straightforward procedure. The one-time option to extend, by one or two years, has to be taken by 1st July 2020 and with the agreement of UK and EU negotiators. It is easy to envisage how a debate over whether to extend could dominate the first six months of the next parliament. A Conservative government seeking an extension would yet again find itself negotiating on two fronts, squeezed between the opposition of many of its backbenchers on one side and, on the other, the EU demanding further UK financial contributions and a carve-out for fisheries as the price.

This would simply lead to six months of politically grinding distraction from the actual matter at hand, which is the future relationship. Ultimately, despite what the Withdrawal Agreement currently says, if both sides believe a short extension is needed at the very last minute, it could probably be agreed – though it might not, which would set up a WTO-terms exit as the default on 1st January 2021.

Secondly, extending begs the question, what would the extra negotiating time be for? Putting UK and EU politics aside, there is a strong economic rationale for a carefully tailored and comprehensive UK-EU deal, with selective regulatory alignment and delicately balanced “rights and responsibilities”.

In 2018, Open Europe proposed that the UK and the EU should aim for an ambitious relationship which would put the UK somewhere between that of Canada and Norway. Broadly, this would mean the UK aligning with EU rules for goods to retain greater access to European supply chains, from which our manufacturers tend to benefit, but diverging for services where EU market access is harder to achieve and where the UK already tends to be more globally oriented.

There is no doubt that a deal of this nature would take monumental effort and tough compromises on each side. Irrespective of time, it is almost impossible to imagine how such a complicated agreement could now be reached given the water already under the bridge.

Many Brexiteers, including the Prime Minister, seem opposed to formalised regulatory alignment per se. Meanwhile, hard-line Remainers have either prioritised thwarting Brexit altogether or insisted on wholesale membership of the Single Market and Customs Union, but with no say.

Above all, as Anand Menon of the UK in a Changing Europe noted to the chagrin of Brexit Twitter last week, everything the EU has done since June 2016 suggests it is loath to adapt its principles in order to have a closer relationship with post-Brexit Britain. EU leaders completely dismissed the UK’s previous attempts to think creatively, by throwing out Theresa May’s Chequers proposals, and have repeatedly presented the UK with a choice between a simple deal akin to Canada’s or the satellite status of Norway. That is the EU’s decision to make, but it does mean that Brexiteers are faced with an easy choice.

Hard-line Leavers and Remainers will both point out that the looser the UK-EU trade agreement, the smaller the economic difference between a deal and No Deal. In which case, why bother at all? It would be a mistake for UK and European negotiators to be so glib.

For both Brexiteers and the EU, Brexit is a constitutional issue, from which economic consequences flow, rather than the other way around. Therefore, devising a new accommodation between the UK and Europe does not simply revolve around the details of trading with the EU. The UK will also need to use 2020 to choose whether to be more or less engaged with Europe via other means, such as bilaterally or in new forums such as Emmanuel Macron’s mooted European Security Council. However, it is likely to be easier to develop a sustainable long-term political and economic relationship between Europe’s nations on the foundation of a UK-EU trade agreement rather than none at all.