Sadiq Khan's clever intervention over Jeremy Corbyn makes him the top candidate for future Labour leader

Khan knows full well that Corbyn is the most likely victor in the leadership race, but he has placed himself to serve as the flailing leader's primary opposition

London Mayor Sadiq Khan, who opened the Night Tube earlier this weekend, has placed himself as a future contender for Labour leadrship

Sadiq Khan has waded into the Labour leadership election delivering a blow to Jeremy Corbyn’s campaign. The Mayor of London had been expected to remain neutral throughout, but he has instead opted to endorse Owen Smith and offer up his brutal opinion on Corbyn, too: he “totally failed” to communicate his message during the EU referendum, and is “unable to organise an effective team.”

Unlike the vocal criticism of other MPs, Khan’s words are likely to have a lasting impact on the future of the Labour Party. His relationship with Corbyn, one suspects, is irretrievably damaged.

The issue for Khan, and for Labour, is that, despite his intervention, the chance of Owen Smith actually winning the leadership election remains negligible. He might pull it off – it would be rather daft to put total faith in the predictions of opinion pollsters after their performance in recent years – but, on the face of it, a strong Corbyn victory remains the most likely outcome of the contest.

If Corbyn wins it is safe to assume he will remain leader until the 2020 election. In which case, we have a situation where Labour’s highest profile and most powerful politician is publicly at odds with his leadership.

All of Corbyn’s opponents (and there are many) will side with the London Mayor. The coming months and years, then, will be characterised by the battle of Corbyn vs Khan. And that is neither good for the party or the country.

We need a Leader of the Opposition who is focused on holding the Government to account and we need a Mayor of London who is focused on working in the best interests of London. The distraction of a protracted popularity contest, a tussle between the two big figures of the party, is a waste of time and energy. Khan’s words have doomed Labour to an even longer civil war than the one to which it had already, ill-advisedly, committed itself.

Khan is an astute politician, however; he knows full well that Corbyn is the most likely victor in the leadership race. But he has placed himself to serve as Corbyn’s primary opposition and the leading candidate for future leadership. If Corbyn goes the distance and Labour, as we can reliably assume, has a calamitous general election in 2020, the position will certainly be vacated. Assuming Khan does a decent job as Mayor, he becomes the favourite to take over.

As one of the most successful and effective politicians of his generation, this claim isn’t so bold. Khan’s record speaks for itself. Besides being the first Muslim Cabinet minister, he was also the mastermind behind Ed Miliband’s successful leadership campaign. He was initially the outsider to be Labour’s London Mayoral candidate, and yet he went on to topple the mighty Tessa Jowell and beat Tory darling Zac Goldsmith in the polls during a tough year for Labour elsewhere.

Khan’s career is still on an upward trajectory. His success is unparalleled within the current Labour Party at the moment. His endorsement of Owen Smith, then, is a statement of intent. What we have just witnessed is Sadiq Khan throwing down his gauntlet. His hat – if you’ll excuse the mixed metaphors – is now firmly in the ring.