On the plus side, Tom Watson is recognisably part of the tale of the democratic Labour Party that must sometimes govern Britain in the settlement that has endured since the Second World War.  He is pro-mixed economy, pro-NATO, pro-EU (as Labour has tended recently to be) and essentially pro-Western – in the tradition of the mainstream of his party since its great victory in 1945.

Though he is, famously or notoriously, a Brownite, Watson is by background and temperament, though not experience, a product of the pre-Blair era: he is basically right-wing Labour.  If he had been part of the previous generation, one could imagine him as a fixer for one of those old right-of-centre trade unions – the EEPTU, say.

On the minus side, Watson has also become part of another enduring story – that of Titus Oates, George Gordon and other charlatans who exploit the fear of minorities.  ConservativeHome gets a lot wrong, but we were right, from the start, about Carl Beech’s – “Nick’s” – wicked and false allegations about Harvey Proctor and child abuse.  Lord Bramall and Leon Brittan were dragged into the claims.  The Henriques report into the Met’s conduct was damning.

Watson has courage, as he showed during the phone hacking controversy, but his conduct over the Beech claims raises the classic knave-or-fool question.  We wrote in the wake of the report that no-one, even in the Labour Party, would ever put their trust in Watson’s judgement again.

CCHQ has been briefing since the Conservative Conference that Watson’s seat, West Bromwich East, was on its target list, although it has basically been a Labour seat since its creation.  It voted 68 per cent Leave; Watson has said that “our souls are Remain”.  Only yesterday, Andrew Gimson reported from the constituency that the incumbent is in big, big electoral trouble.

Watson is coy about his reasons for departure, but the fear of losing his seat must be one of them.  There will be wider reasons.  In the fissiparous struggle between Labour’s Left, now in the form of Momentum, and the rest of the party, Watson, the ultimate Labour fixer, lost out.

He cannot have been happy at the prospect of seeing the party’s leader, a product of the anti-West culture that is alien to him, an election away from Downing Street.  His departure thus raises a question for members of the Future Britain Group, the alliance of moderate Labour MPs which he helped to form, as well as much of the rest of the Labour Party.

Which is: while Boris Johnson is leading a Party that, with the exception of EU policy, Macmillan would recognise were he still around – pro-infrastucture, pro-higher spending, conventionally green, pro-migration for the “brightst and best” – Labour is fronted by a man whose leadership has opened Labour’s door to anti-semites, extremists, Far Leftists and Islamists, all of which share a culture hostile to western liberalism.

Are other centrist Labour MPs really prepared to do other than Watson has now done, and now recommend to the British people, in the form of their candidacies, that Jeremy Corbyn become Prime Minister?  Are the Hillary Benns and Yvette Coopers really willing to do so?