Jeremy Corbyn has been prime minister for barely a couple of hours. He has returned from Buckingham Palace, where the Queen invited him to form a government, and has given his first triumphant speech in front of No 10, promising that he will bring change and govern for the many not the few. The pound has not collapsed but it is certainly trembling. And as investors attempt to absorb the news, John McDonnell slips out of Downing Street and makes the short walk to the Treasury. Only now is the fate of the economy to be determined.

The new chancellor will be applauded into the building by the waiting staff and shown up to his new office by the permanent secretary, Sir Tom Scholar. There