Donald Trump’s visit to the United Kingdom for the Nato summit gives physical form to the argument that Labour want to make about the health service: that Boris Johnson will sell off the NHS to American companies.

Are they right? The Conservatives have promised that the NHS and British agriculture will both be kept out of any US-UK trade deal. Labour’s big leak — that government document describing the priorities of American and British trade negotiators — does not prove that they intend to break that promise, anymore than the presence of steak on a menu when you sit down for dinner proves that you intend to eat beef that evening.

But the reality is that if you want a deep and meaningful US-UK trade deal, both those promises are going to have to go. The argument that some optimistic Tories, who want a US-UK deal and know that Johnson's promises cannot be reconciled with one, are making is the same as the one that Labour makes in private: once a parliamentary majority is in the bag, those pledges about food and pharmaceuticals will be broken faster than you can say “no customs and regulatory border in the Irish Sea”.

No one can say for certain if they are right — but my feeling has always been that no matter how big the Conservative majority, the political toxicity of a deep and meaningful US-UK trade deal — which would in any case add less than one per cent to the UK's GDP means that one will never be struck. That’s the real problem with Johnson’s trade plans: he pledges to take us out of the customs union and single market, but has also made a swathe of promises that make it hard to see how he will ever strike trade deals of the depth and value necessary to replace the loss of EU-UK trade.