Tom Watson is the alternative leader of the opposition as well as the deputy leader of the Labour Party. Because he has his own mandate from party members, he can speak for the other part of a divided party.

Many of the thousands who marched today will have voted for Mr Corbyn as Labour leader. Many of them will have been inspired by the message of hope and change of his “straight talking, honest politics”.

And many of them will have been disappointed by his equivocation on the question of Europe and in particular his obfuscation over giving the British people the Final Say on the terms of Brexit.

So they will be grateful to Mr Watson for giving voice to this growing demand for a democratic check – one that is supported by the overwhelming majority of Labour Party members, a large number of Independent readers and a significant proportion of public opinion.

Unlike Mr Corbyn, Mr Watson is clear that a fresh EU referendum is “the only way” to solve the crisis. And while Mr Watson’s words to the crowds today were ostensibly directed at the prime minister, many of them seemed aimed just as much at the leader of the official opposition.

“At every turn we have been ignored,” he said. “At every stage Theresa May has doubled down rather than reaching out. The way to solve this crisis is to recognise we’re all in it together. The way to break the stalemate is for parliament and the people to come together.”

Mr Corbyn should heed those words. Just as Ms May should engage in dialogue across party lines in the House of Commons, so should the Labour leader put aside factional differences and reach out to all who share a progressive vision of Britain’s place in Europe.

Mr Corbyn’s refusal to take part in a meeting attended by Chuka Umunna, spokesperson of The Independent Group of MPs, was a significant and depressing moment this week.