Sir Peter Marshall was Commonwealth Deputy Secretary-General 1983-88 and UK Permanent Representative to the UN in Geneva 1979-83.

I think I must be just about the only person on this side of the Channel who has made a detailed study of the EU Guidelines of 29th April this year, issued in response to the Prime Minister’s letter of 29th March, triggering Article 50.

Their disturbing substance originally prompted me to write to Donald Tusk. The course of the negotiations in Brussels between David Davis and Michel Barnier, combined with the anaemic reception accorded by the EU to the Prime Minister’s speech in Florence, raises the spectre that the EU is not really interested in reaching a constructive agreement with the UK .

During my diplomatic career, I was involved in a considerable amount of international negotiation over major issues of policy, and I can say, with hand on humble heart, that I have never seen, or even heard of, a document so unconstructively negative as the Guidelines.

We are familiar with very tough starting positions, destined to be abandoned,  in part or as a whole,  as the negotiations proceed. But that is not what we are up against here. The Guidelines carry the authority of the European Council. We witness their inflexible interpretation by the European Commission. They seem to constitute some form of FestungEuropa. Unless they are modified in some way at the next meeting of the European Council on 19th-20th October, we are in for trouble.

The present impasse is not merely a great sadness.  It is an incipient international tragedy.

The European Union is a great institution.  The contribution to peace and reconstruction in Europe , after the calamity of two world wars in relatively quick succession,  made by the combination of the noble reconciliatory statesmanship of Robert Schuman and the pragmatic genius of Jean Monnet can hardly be overstated.  But, for reasons which will long engage the close attention of historians, the Union has lost its way in recent years.

Emmanuel Macron’s recent speech at the Sorbonne was the most far-reaching survey of the situation ever made by a European head of state.  Its review of the past is masterly.  Its prescriptions are nothing if not bold.

As far as we are concerned, the President of the Republic speculates that, some time from now,  the UK might feel that it could find its place in an EU reformed in the manner which he prescribes.  Would it were so.

Paragraph five of Article 50 addresses the possibility that a member state, having withdrawn, asks to rejoin: “its request shall be subject to the procedure referred to in Article 49”.  In plain terms, the errant ex-member state is brusquely directed to take its place in the queue at the back door.  No Prodigal Son treatment is available.

But it is our previous experience that will surely deter us permanently.  We were not among the founder members of the EEC, established in 1957 by the Treaty of Rome.  We realised our mistake and applied to join in 1961.  In 1963, to universal astonishment, at a stage when the general assumption was that the accession negotiations were on the verge of successful completion, de Gaulle announced at a press conference at the Elysee that the UK was unfit for membership. The negotiations collapsed.

We were kept out for a decade.  When we eventually joined,  the terms of accession were so onerous that Margaret Thatcher insisted on, and in the end obtained, a substantial rebate, part of which Tony Blair later waived, in a co-operative gesture that went very largely unacknowledged by our partners.  Whenever “divorce bills” of extravagant size are mentioned in the Brexit context, it is worth recalling the unhappy tale of the nuptials.

The EU is negotiating with the British people.  It knows that, on the basis set out in the Prime Minister’s “trigger” letter and in the Florence speech, we are playing full and fair. They expect a measure of reciprocity from our partners, to whom we have contributed so much in the past, and with whom they profess to desire close partnership in future.

Let us all rally behind Theresa May in her endeavours on our behalf, pausing only to cheer Ruth Davidson loudly for her glorious rebuke of some recent Tory playground-plotting.