A funny thing happened to me last Monday. I was lunching with my friend Sir Samuel Brittan, the great Financial Times economics commentator, in advance celebration of his 86th birthday. It was he who, when we were colleagues on the FT, suggested that I specialise in writing about the economy.

During the lunch, several anti-Brexit sympathisers approached our table to express approval of the slogan on my pullover. It was the present from one of my daughters that I referred to here two years ago, which proclaims in large letters: “All I want for Christmas is EU.”

At the end of the meal there was a general, and not especially discreet, discussion about how awful the situation was and, in particular, how disgraceful the behaviour of the man who is now our prime minister. At which point a nearby diner left the restaurant and one of the waiters said: “Do you know who that was? Johnson’s mother.”

Yes, Alexander Johnson, the man who campaigned all too successfully on the slogan Get Brexit Done, but who, according to reports, has now banned government officials from using the very word Brexit on the grounds that it is “time to move on”.

There are those Remainers who take comfort in the thought that in due course the principally pro-Remain younger generation will see its ranks swollen and demand that we should acknowledge this historic mistake and apply to rejoin the EU. But those of us who recall how difficult it was to join in the first place – our application was turned down twice by General de Gaulle – think this is far too optimistic. I was therefore heartened by the Christmas message from Frans Timmermans, the deputy president of the European commission: there has been damage already, and there will be more to come, but the UK “will always be welcome to come back”.

The loss of tax revenue likely to accompany the mere approach to Brexit makes Johnson’s electoral promises for the north look, well, ridiculous

Michel Barnier, the EU’s chief negotiator, has made it clear that a year’s transition period is perilously short for negotiating future arrangements – and, indeed, that the kind of Trumpian departure from EU regulations envisaged by Johnson, Dominic Cummings and their ilk is non-negotiable with the EU. The stage is therefore set for a year’s fooling around, followed by a no-deal crash-out. This at a time when Johnson is promising a golden future for the former Labour supporters in the north of England and Midlands who have supposedly lent him their votes.

So what kind of economy and outlook does Johnson inherit? As regular readers know, I did not get where I am today by making economic forecasts – the old economists’ joke is that it is difficult enough to forecast the past – but I take note of all the forecasts being made by reputable economic institutions, and they are almost all terrible. The loss of tax revenue likely to accompany the mere approach to Brexit, let alone the expected crash-out, makes Johnson’s electoral promises for the north look, well, ridiculous.

Consider: in the days when Brittan and I were covering economic crises such as the notorious three-day week, the average annual growth of productivity in this country was 2-2.5%. The average growth of productivity in the 10 years since the financial crisis of 2007-09 has been 0.3%. Paul Johnson, the director of the Institute for Fiscal Studies, points out that, under successive Conservative governments (including the coalition) since 2010, the cuts in public services (other than the NHS) have amounted to 21%. No wonder we see social chaos all around us.

Now, I am going to break my rule and make a forecast. It is a forecast of what should happen, but won’t. When Johnson returns from the West Indies and moves on from victory celebrations to the hard study of what his officials tell him, he should realise that his campaign promises are totally incompatible with the appalling economic outlook threatened by the word he does not want his officials to use.

He is no Churchill, although he thinks he is, but he could do worse than study that phenomenal book by Tim Bouverie, Appeasing Hitler. Hitler was the biggest threat facing Europe, and Churchill knew it. While not wishing to compare the threat of Brexit to the threat of Hitler, I think the point is that Hitler’s intentions were always clear for those with eyes to see and ears to hear, and so are the prospects for leaving the single market and pretending we can go back to the 19th century.

What Johnson should do, now that he has achieved his childhood ambition to become prime minister, is grow up, become a statesman and be big enough to say he has made a mistake. He won’t, of course. An easy forecast.

Happy new year!