Theresa May has volunteered to organise the greatest disturbance to British political and economic life since the Second World War. She has to make sense of her own phrase “Brexit means Brexit”, which was her way of reassuring the winning side in the EU Referendum debate that, although a cautious Remainer, as Prime Minister she would obediently implement the national will. But neither the final shape of Brexit nor the route to reach it has been specified.

Lord O’Donnell, the former Cabinet Secretary, has done the Prime Minister the considerable favour, in an interview in The Times, of decisively clarifying one tricky aspect of the Brexit scenario. It does not mean the instant repeal of every detail of EU law that has accumulated over the last 40 years – no Year Zero. That would be administratively chaotic, and would leave gaping holes in the regulatory regime which businesses need if they are to function.