Councillor Matt Hartley, Conservative group leader on Labour-run Greenwich Council, completed the London Marathon on Sunday. While still going downstairs sideways and being assailed by bizarre food cravings – well, that’s what’s happened to me for three days after each time I’ve run it – he was chosen as the latest Tory to try to prise the marginal Eltham constituency away from Labour’s Clive Efford. How much further exertion might this require?

Like Hammersmith, Tooting, Dagenham and Rainham and Westminster North, Eltham defied expectations that it would turn blue in 2010, and Efford increased his majority to 2,693 two years ago. The former black cab driver and alumnus of Walworth Comprehensive has held the seat since 1997. Tories have conceded in the past that he has credibility in Eltham’s a mix of commuter suburbs and council estates.

But the threat he faces this time looks far greater than the one he saw off in 2010. A new national poll gives the Tories a massive 23% lead, which is even higher than before the election was called. By contrast, Labour might still be just ahead in London overall, but Eltham is one of around ten seats they could lose.

The millstone of Jeremy Corbyn, whose London approval rating was recently measured as a miserable -44%, is likely to weigh more heavily in this part of town than in the London of brown rice and bicycles where Corbynism has its roots. Expect Hartley to point out that Efford was one of the Labour MPs whose nominations enabled Corbyn to get on the leadership contest ballot after Ed Miliband’s resignation.

He must surely be regretting that now. That said, he can legitimately claim it was an act of charity rather than ideological fellowship. Efford, who has never been of the hard Left, gave a public bollocking to Old Wykhamist Corbyn backer James Schneider last year and has recently led the re-founding of the parliamentary Labour Party’s centre-left Tribune group.

His Twitter timeline shows him highlighting the bedrock Labour issues of health, public transport, schools funding and free school meals, which ought to resonate locally. It also shows him supporting Gerard Coyne against Corny-backer Len McCluskey in the recent battle to lead Unite and saying Momentum founder Jon Lansman should set up his own party “instead of misleading honest Labour members”.

Hartley, meanwhile, has hardly had time to lace up his election running shoes, but he’ll soon by re-pounding the streets of Shooter’s Hill. If Efford holds him off, it will be an impressive result.