So there will be a temptation for the BBC to tell Mr Trump: "See you in court." That, though, could backfire spectacularly even if the BBC went on to win.

Under the rules of discovery Mr Trump's team would be entitled to demand access to internal BBC communications about Mr Trump.

It is beyond doubt that lots of BBC employees find Mr Trump repellent, so would the BBC be willing to run the risk of allowing Mr Trump to see what its staff say to each other about him? If the BBC had to hand over emails that mention Mr Trump, would those emails also contain disparaging comments about other public figures? Like Mr Trump's friend Nigel Farage, perhaps?

Mr Davie and Deborah Turness, the chief executive of BBC News, resigned in the wake of The Telegraph's revelations, but plenty of people who are still at the BBC might rather not have their emails raked over by Mr Trump's legal team.

One former BBC staffer said: "I'm pretty sure the BBC will want to do anything they can to avoid having to disclose what people have said about Trump in internal messages.

"And even if people at the BBC have been careful about what they put in writing, the US court would presumably want to see any emails from the external production company involved in making the Panorama documentary, which would be outside the BBC's control."