Dominic Cummings must go for a clear breach of a lockdown that he helped to draw up

This, Boris Johnson said, was before Mr Cummings and his wife were incapacitated by Covid-19.

Had the PM left his comments there, it would have been a wholly unsatisfactory explanation for what Mr Cummings did. But Mr Johnson went on to say that his key advisor had behaved “responsibly, legally and with integrity”.

The Tory leader is dependent on Mr Cummings, who is an architect of Brexit, and of the Conservative victory last year nationally and, specifically, its success in northern Labour heartlands.

Mr Cummings is an abrasive character. We do not know if he ever actually said “I don’t care if Northern Ireland falls into the f****** sea” as was reported. The concern, after Boris Johnson’s betrayals over the internal UK border and then the PM’s evasions as to what he had agreed, is that such thinking does exist in some quarters in Downing Street.

If so, it deserves the deepest contempt of anyone who values the United Kingdom.

Mr Cummings is an original thinker with radical and interesting ideas about shaking up the bureaucracy of government. But the PM’s response yesterday was not only inadequate, it did great harm to the government.

The public support for the massive damage and sacrifices of lockdown has been high. People have given up funerals for loved ones and lost their businesses and jobs.

Those who help oversee lockdown must observe it. Catherine Calderwood, the Ulster-born Scottish chief medical officer, was right to quit when she breached rules, Professor Neil Ferguson of Imperial College likewise and also Mike Nesbitt MLA, who stood down from a Stormont committee.

Mr Cummings’ trip is the worst of those breaches. He drew up the rules.

He must go. He might in a year or two be able to return but for now his position is untenable.

Backbench Brexiteer Tory MPs can see this, and so should the PM.