In answers to questions following his statement in the Commons on Monday, Boris Johnson let drop an interesting statistic. He said that, ‘on busy days’, more than 400 officials work in 10 Downing Street. This figure explains a lot — why so many staff there got Covid, why, after long hours in overcrowded conditions, they might want to open bottles of wine, why factions struggle for mastery and leak against each other, and why the heart of government suffers from clogged arteries.