Emily Thornberry is tipped to be the first female leader of the Labour Party

The second most significant thing that happened in politics last week was a report about the leader of Britain’s biggest union. (The most significant thing was Boris Johnson’s subdued leadership bid on the Today programme on Friday, about which I have written already.) Paul Waugh of Huffington Post reported on Thursday that Len McCluskey, the general secretary of Unite, “has told friends that he thinks Emily Thornberry is a unifying figure who can carry on Jeremy Corbyn’s work when he eventually decides to step aside”.

Waugh quoted a “senior source” who said: “Of course, there is no vacancy and there won’t be for the foreseeable future. Len totally backs Jeremy and wants him to be Prime Minister. But the next Labour leader after Jeremy has to be a woman and Len believes Emily is a unifying figure.”

Thornberry, the Shadow Foreign Secretary, raised her profile last month when she stood in for Corbyn at Prime Minister’s Questions, and impressed her own side with her confidence and humour, quoting all the contradictory things that ministers had said about the prospect of not being able to agree a Brexit deal with the EU.

But what on earth is McCluskey up to? The most plausible explanation is probably: nothing. He may have said to some people that he sees Thornberry, the Shadow Foreign Secretary, as a “tough cookie who isn’t afraid of taking big decisions”, because that is what he thinks. He may not have expected it to be reported.

But even if that is merely his opinion rather than a deliberate attempt to throw his political weight behind her in public, it is deeply intriguing. It means that he is thinking about the succession at a time when Corbyn carries all before him and shows no sign of flagging. On the contrary, Corbyn looks years younger than 68 and could easily lead the party into an election in five years’ time.

It means that McCluskey is not so taken by Rebecca Long-Bailey, the Shadow Business Secretary, who was thought to be favoured by John McDonnell, the Shadow Chancellor. By saying the next leader “has to be a woman”, McCluskey also neatly rules out McDonnell himself, who, despite a heart attack in 2013, might still harbour ambitions for the top job. And it means that McCluskey has failed to “tell friends” that he thinks Angela Rayner, the Shadow Education Secretary, could be the next leader.

Thornberry is currently fourth favourite at the bookies, behind Keir Starmer, Yvette Cooper and Clive Lewis. But McCluskey’s endorsement should put Thornberry out in front. Unite does not have the influence it once had in Labour leadership elections, now that the unions’ affiliated supporters have been so outnumbered by the members and supporters attracted by Corbyn, but it still has money, organisation and phone banks.

Her name has also been mentioned as a possible deputy leader of the party if the rules are changed to require a second deputy leader who must be a woman. But would this be enough?

Her self-confidence is remarkable. From her sacking by Ed Miliband as Shadow Attorney General for posting a sneering photo on Twitter of a house bedecked in flags of St George in the Rochester by-election in 2014, she has risen to be Corbyn’s de facto deputy, given that Tom Watson, the titular deputy Labour leader, is not a Corbynite.

Thornberry's status as in effect Corbyn's deputy was confirmed recently by her promotion to Shadow First Secretary of State, in addition to her post as Shadow Foreign Secretary (she was up against Damian Green, the actual First Secretary of State, at Prime Minister’s Questions on 12 July). The Labour Party website lists her on its Shadow Cabinet page only as Shadow Foreign Secretary, which is also how she is listed on the official Parliament website.

However, a Labour spokesperson told The Independent today: “Emily Thornberry is Shadow First Secretary of State and Shadow Foreign Secretary.”

I get the impression she thinks she is the leader in waiting. She was recently interviewed on BBC Radio 4 Westminster Hour and failed to mention any colleague by name, not even her leader. Now it seems that McCluskey, the leader of the most powerful union in Labour politics, thinks she is the leader in waiting too.