I know that Theresa May is beleaguered on all sides – not least her own – but did she realise what she was saying when she “warned” the Conservative conference that divisions over Brexit “could stop the UK leaving entirely”?

Since stopping the UK leaving entirely is just what we Remainers wish to achieve, one can but marvel at the prime minister’s pronouncement. I am tempted to add “long live the divisions”, but the truth is that the sooner this Brexit fantasy is put to rest, the better.

My old friend Sir Mike Rake, the former president of the CBI, recently warned a City audience that we were on the verge of an economic and constitutional crisis. He is not given to hyperbole, and speaks for many businesspeople who live in the real world, and not on the Planet Fantasy occupied by Boris Johnson, Jacob Rees-Mogg and their ilk.

It was bad enough when the chancellor, Philip Hammond, held out the prospect last week of a “deal dividend” the Treasury cannot possibly believe in. There is hardly a respected economic institution that concludes, after rigorous analysis, that Brexit would do anything other than reduce the British economy’s underlying growth rate.

Far from there being a prospective dividend from Brexit, the government’s own analysis earlier this year concluded that any form of Brexit would in effect be an own goal. Over a 15-year period the so-called Canada-type free-trade deal could result in a loss of almost 5% of GDP, and Theresa May’s “no deal’s better than a bad deal”, relying on WTO rules, would be likely to result in a loss of almost 8%. Even the much-discussed Norway option – continued membership of the European Economic Area – would involve a loss of 1.6%, as well as a loss of influence over EU decisions.

There is no such thing as a Brexit dividend. The only possible dividend would result from the abandonment of the entire Brexit project so that investment which has been held up during this period of dreadful uncertainty can be implemented.

As for those markets outside the EU, all the evidence from trade experts is that proximity of markets is what really matters. Sir Brian Unwin, honorary president of the European Investment Bank, pointed out in a recent lecture: “Ironically, in view of the fanciful talk of switching from Europe to become a more global trading nation … over the past year exports and imports to and from the EU have increased faster than those goods to and from non-EU countries.”

Another Brexit dividend, we are told, is that it would herald the end of austerity. Older readers will know that I regard the austerity policy as having been misconceived from the start. Indeed, it has contributed to the reduction in the UK’s underlying growth rate, as well as to the erosion of public services. We don’t need Brexit to end austerity.

In which context I think the leaders of both main parties should take note of an article earlier this year in the journal of the Royal Economic Society by the veteran British economist Robert Neild. In To Tax or Not to Tax? The Truth about Taxation, Professor Neild tells it as it is: “In Britain public services are falling apart. Our health and social care services are deteriorating; crime rates are soaring, and so are violence and suicide in prisons; the quality of our schools is uneven and unfair; state pensions are miserly; poverty and homelessness are increasing … On all sides we are confronted by social injustice and economic neglect.”

Everyone, including my old Brexiter friend Lord Lawson, knows public services are much better on the continent. Why, Lawson has even taken up residence in France. Neild pinpoints the explanation: a preparedness to pay for public services. The tax take as a percentage of GDP is 40% on average in the EU and 47% in France. You get what you pay for! In the UK it is 35%.

Now, in his “deal dividend”, Hammond talked of “a balanced approach … between keeping taxes low, supporting public services, reducing the deficit, and investing in Britain’s future.” Neild points out that since public expenditure is about one third of GDP, an increase in taxation of 1% of GDP makes possible approximately a 3% increase in public expenditure. Thus a 5% increase in the tax take, from 35% to 40%, would pay for an increase in public spending of almost 15%.

The Tories are obsessed by lower taxes, and Labour by higher taxes provided the money comes from the rich and tightening loopholes. Neild’s message is that to bring services up to scratch, there needs to be a general increase in the willingness to cough up.

We need to stop Brexit and come to grips with the many economic and social problems that have been sidelined during this terrible diversion.