Boris Johnson’s fascination with the life and times of Winston Churchill is well known. So it was clever of the European commission’s new president, Ursula von der Leyen, to recall on Wedneday how, in 1946, the prime minister’s hero once made the case for a “United States of Europe”.

Churchill’s famous intervention helped build the momentum that led to the formation of the European economic community. Ms Von der Leyen, in a speech which preceded a Downing Street meeting with Mr Johnson, said that his postwar call for a new European family remained the best case made for the union. But she acknowledged that, three and a half years after the prime minister successfully campaigned for Vote Leave, the divorce deal between Britain and the EU was “done and dusted” and it was time “for the best and oldest friends to build a new future together”.

A confirmed anglophile, Ms Von der Leyen’s charm offensive came ahead of crucial talks on what shape that future would take. The warmth of her words was disarming and effective. But Churchill’s position on the United Kingdom and Europe was perhaps a little more complicated than her speech implied. Britain, he wrote in one essay, “is with Europe, but not of it”. It is “linked, but not comprised”. Working out what that might mean, in the context of Brexit and the 21st-century global economy, is a fair summation of the task ahead for Mr Johnson. In charge of a parliamentary majority that gives him licence, Britain’s future prosperity depends on the conclusions that he reaches. The country must hope that in the months ahead, behind the inevitable prime ministerial bluster and can-do bonhomie, a sense of sober realism will kick in.

At this stage, there is scant evidence of that. By writing into law that Britain must exit the agreed transition period by December, Mr Johnson has needlessly imposed a timetable that limits the scope of what can be achieved in the coming negotiations. His claim that a new cliff edge will give Britain leverage in Brussels and EU capitals is specious. It is far more likely that humble pie will again be consumed in Downing Street, as it was last autumn when the prime minister caved at the 11th hour on the principle of a customs border in the Irish sea, in order to “get Brexit done”. For businesses desperate to retain close and fluid relationships with Britain’s biggest and closest trading partner, that could be no bad thing. Ms Von der Leyen made it clear again on Wednesday that the UK’s freedom to economically diverge from the EU will come at a high price in tariffs, quotas and customs barriers. There will be no squaring this circle. If he is wise, Mr Johnson will acknowledge this and calibrate demands accordingly.

If he agrees to close regulatory alignment in vital sectors such as cars, aerospace, chemicals, food and drink, and pharmaceuticals, a basic free trade deal may be possible by December. But the status of Britain’s service economy, which generates the bulk of the country’s wealth, is unlikely to be resolved by then. The same goes for the politically fraught areas of agriculture and fishing, and the implications of the government’s stated intention to end the free movement of EU citizens into Britain. The alternative to a bare-bones deal would be to crash out, hobbling the economic prospects of a supposedly free and “global” Britain. But Mr Johnson’s majority means he has sufficient room for manoeuvre to ignore the siren calls from his party’s Brexit theologians. To follow their advice would be a very high price indeed to pay for “taking back control”.