It wasn’t meant to work out this way. A month ago, Westminster watched to see if Jeremy Corbyn could get the support of the 35 MPs he needed to enter the Labour leadership race. At the time, it seemed a sort of joke. After all, the people who were lending him their backing weren’t doing so for any great love of Corbyn. As a rule, they either wanted a ‘broad debate’ or thought that the ritual slaughter of the left-wing candidate would make it easier for the new leader to move the party to the centre.

A month on, things look very different. Corbyn now has the endorsement of Unite, the most powerful union in the country, and several others. He has the second highest number of constituency Labour party nominations, his campaign is churning out impressive-looking literature, and sober-minded Labour insiders keep revising upwards how well they think Corbyn will do. Most worryingly for those who want a Labour party that can win elections, Corbyn is dragging the race to the left. One shadow cabinet member laments, ‘It is the Death Star. It is dragging Andy and Yvette in.’ This frontbencher adds, more in anger than sorrow: ‘I feel for them. They’ve got to think about second preferences.’

So a candidate everyone assumed would show the limited appeal of hard-left positions within the Labour party appears to be showing the exact opposite. At the hustings and in televised debates, Corbyn is getting more than his fair share of applause. Meanwhile, Liz Kendall — the soi-disant Blairite candidate — is having to defend herself against the charge that she’s a Tory.

Some could see this coming. When I bumped into one shadow cabinet member on the reformist wing of the Labour party just moments after Corbyn had made the ballot, he was almost speechless with rage. After shaking his head vigorously, he said: ‘We’re in real fuckeroo territory now’, before stalking off still shaking his head.

This anger is understandable. Corbyn is a throwback to the hard-left Labour politics of the 1980s: he is far closer to Tony Benn than Tony Blair. He refuses to say what the limit should be on the top rate of tax and is prepared to talk about Hamas as his ‘friends’. A Labour party led by Corbyn would end in a defeat that would make Michael Foot’s loss in 1983 look modest.

There is, though, one consolation for Labour MPs: no one knows how real this Corbyn surge actually is. This leadership contest is taking place under new rules and with a new electorate, so it is hard to be sure how things are going to turn out. No pollster is confident of calling the race. One senior Labour figure wonders if the Corbyn bandwagon is just part of the distortion effect of social media. ‘Is it just the kind of Twitter thing that would have made you think that Labour was going to win the election?’

There are good grounds to think that Corbyn’s success is more than a 140-character phenomenon, though. Rival campaigns claim that their canvassing has him doing well, noticeably better than Liz Kendall. Now there is an element of gamesmanship in these remarks — both the Burnham and Cooper camps want to do down Kendall. But combine this with the Unite endorsement and the audience reaction at the hustings, and it does seem that Corbyn’s reach extends beyond the digital world. One of those who has crunched the numbers asks, ‘Does Corbyn come third or second? That’s the question, unless something changes.’

One Labour insider is convinced that Harriet Harman’s recent troubles over welfare are a direct consequence of Corbyn’s success. This source says that Corbyn’s prominence in the debate has forced Burnham and Cooper to the left, making them break with Harman, who has said she agrees with the plan to limit child tax credits for new claimants. The Tories are delighted about this, gleefully pointing out that this measure is one of the most popular in the Budget.

But there is something deeper going on here. Labour has become a party that is happy to talk to itself, not the country. When Burnham turned up to Gay Pride, he did so wearing a T-shirt boasting, ‘Never kissed a Tory’. It was a small thing, but a revealing one. It showed a man who’d rather revel in self-righteousness than look for converts.

By contrast, the Tories are trying to win over new voters. They have moved to the political centre, as the announcement of the national living wage made clear, and this week David Cameron announced a campaign to close the gender pay gap. The Tory plan is clear: occupy the centre ground and force Labour to the political extremes.

Labour have spent so long trying to portray George Osborne as an ideologue on the deficit that they have missed the fact that he is a deeply pragmatic politician. By again extending the period over which the books will be balanced, Osborne has softened the impact of the cuts. The Budget will still be in surplus by the time of the next election, ensuring the Tories can claim that any Labour commitment to spend more will tip the country back into the red.

But there is a spectre haunting the Tory party: Europe. To usher in a new era of Tory majority politics, the party first has to get through the EU referendum without ripping itself apart. At the moment, things do not appear promising on that front. The deal that Cameron is currently seeking would not be sufficient to prevent a Tory split on the issue. Boris Johnson is publicly flirting with voting Out, and the Out campaign is preparing to start recruiting Tory activists to the cause.

Another worry for the Tory leadership is that because of boundary changes and a reduction in the number of parliamentary seats, many Tory MPs will have to compete for re-selection. Many might imagine that the most effective way to boost their chance of being chosen by a local association is to campaign for Out.

Yet Cameron and Osborne’s hope must be that the prospect of another Conservative majority government is enough to contain the coming row over Europe. With Labour moving left, the next election looks like being the Tories’ to lose.