At a friend’s wedding celebration on a remote Swedish island last weekend, I kept being approached by baffled Swedes. Their recurring refrain was: why is your country doing this?

Sweden is a fellow member of the European Union and, in common with the UK, enjoys “the best of both worlds”. Like us, at the moment, it possesses all the advantages of EU membership, not least from belonging to a powerful trading bloc: it is also not a member of the eurozone, whose economic policies have been far too deflationary. The recent recovery in the eurozone is to be welcomed, but by no means justifies the previous policies that aggravated unemployment in so many countries, especially Greece.

I notice, by the way, that Theresa May, whose public statements continue to be all over the place, has recently resorted to that last refuge of a scoundrel: comparisons of the state of this country after the 2007-08 financial crisis with that of Greece, in a dubious attempt to justify “austerity”.

Now, one of the many rival, or complementary, explanations for the recent election result was that it constituted a final revolt against austerity. The Labour party under Jeremy Corbyn and John McDonnell most certainly struck a chord with its emphasis on the economic and social damage George Osborne’s austerity policies have wrought – and which, despite some minor concessions, are still largely in force.

The economic miracle that was supposed to follow austerity has most certainly not occurred. Every day brings news of economic slowdown and mounting concern at the Bank of England about the wisdom of tightening monetary policy in the face of the gathering British economic storm.

Yet the Conservatives in parliament seem to be dominated by a powerful minority of ideological Brexiters who are determined that these so-called negotiations with the other 27 will end in tears. They would then pursue their fantasy of going back decades – or, in some cases, centuries – and starting trade negotiations again from a position of manifest weakness. I wish I were making this up.

It is patently obvious that the Conservatives were hopelessly ill-prepared for the current negotiations. By contrast, I am authoritatively told that from the moment the decision to hold a referendum was announced, contingency plans began in Brussels for the Brexit our partners did not want but, wisely, as it turns out, feared.

It is patently obvious that in this crisis, the 27 are fielding premier-league negotiators, whereas we have less gifted amateurs such as Boris Johnson telling them to “go whistle”.

Johnson fancies himself as a classicist, so he will no doubt appreciate a new book entitled Guilty Men by an author who adopts the pen name “Cato the Younger”. Born in Rome in 95 BC, the original Cato the Younger warned the leaders of Rome about the risks of folly. If ever there were a greater economic and political folly than Brexit since we were finally allowed in to what is now the EU in 1973, I have yet to hear of it.

Older readers will no doubt recall that Cato the Younger was adopted as a pseudonym by the young Michael Foot in a book also entitled Guilty Men, to attack the appeasers in the late 1930s on the eve of the second world war.

Foot’s pseudonymous successor regards the Brexiters as the modern version of the appeasers, and quotes Churchill: “The use of recriminating about the past is to enforce effective action at the present.”

Which brings us to a potentially historic role to be played by the present Labour leaders. This role would involve the burial of an awful lot of hatchets, and a revision of long-standing far-left beliefs.

Thus: much is being made of comparisons between the Corbyn/McDonnell Labour party and the 1983 Labour manifesto, the notorious “longest suicide note in history”, which included a commitment to leave the EEC.

Strangely enough, among the paid-up subscribers to that manifesto were the then leader, Foot, Neil Kinnock and Jeremy Corbyn. I got to know Foot well in his old age and he became a passionate pro-European, as did Kinnock.

At this potentially disastrous moment in our history, it is time for Corbyn and McDonnell to move on – indeed, from some of his public remarks, I deduce that McDonnell is more prepared to move against the whole idea of Brexit than Corbyn.

The point is that Labour has captured the imagination, and support, of the young who, unless the whole idea of Brexit is rescinded, will have to suffer the consequences of their elders’ vote to make the country poorer.

My old friend, the former Guardian Brussels correspondent John Palmer, has been hard at work trying to advise the Labour party unofficially. John is another former international socialist turned passionate pro-European. But Sir Stephen Wall, author of the definitive history of the years leading to our joining the EU in 1973, points out that Labour has so far been cultivating Brexiters, as well as Remainers. The party may think this is part of a brilliant electoral stratagem but, from now on, it is simply not good enough.

If Corbyn and McDonnell want to consolidate the young vote and save the nation from an historic folly, they have to commit to stopping Brexit in its tracks. Apart from anything else, the damage wrought by Brexit would almost certainly negate their plans to counteract the travails of austerity.

We need countervailing action soon. Every day brings evidence that the mere prospect of Brexit is damaging a British economy that is in enough trouble already.