Exclusive: Leaked files offer a glimpse of the ex-prime minister’s relationship with Christopher Harborne

As he boarded the night train to Ukraine, Boris Johnson had the usual entourage of aides and bodyguards – plus the man who had given him £1m.

Less than a year had passed since Johnson accepted what is thought to be the largest donation ever to an individual MP. It was from Christopher Harborne, one of the UK’s biggest and most private political donors.