For most ordinary people, the British summer traditionally comes to an end with a rain-soaked bank holiday. For the Westminster political class, a signed article by a cabinet minister in a national newspaper carries much the same autumnal associations.

George Osborne was doing the honours on Monday. Ostensibly, the chancellor was promoting a relatively technical announcement about infrastructure investment at the Faslane naval base in Scotland, but in practice he was marking the resumption of conventional Conservative/Labour hostilities after an August that has seen Tory HQ mostly on autopilot, content to let Labour tear itself apart.

The Commons does not start sitting again until next Monday, but David Cameron has also been putting his name to a newspaper op-ed – he has a piece in the Times on Tuesday – and he is back from his holiday in Cornwall. Westminster politics is getting back to normal.

In his Sun article, Osborne said, although some were treating the contest as “a bit of a joke”, he thought it should be taken deadly seriously. Without mentioning Jeremy Cobyn by name, he said “an unholy alliance of Labour’s leftwing insurgents and the Scottish nationalists” were “the new unilateralists of British politics” and that they posed “a threat to our future national security”.

For most of the summer, the Tories said very little about Corbyn, or anyone else in the Labour leadership contest. But now that many Labour members and supporters will have cast their vote (the result due on Saturday week), Osborne is keenly aware that a new leader saddled with a negative image from the beginning will find it hard to escape such framing. As such, the Faslane visit can be seen as the first step in a Tory operation to define Corbyn as a peacenik security risk.



If the Islington North MP does win, as the polls suggest, the Tory onslaught will go much wider, covering vast tracts of his policy agenda. But Corbyn’s unilateralism is a particularly attractive target for the Tories because a large number of Labour MPs strongly support the nuclear deterrent and would probably defy the whip if ordered to vote against its renewal.



The main Commons vote on renewing Trident does not have to take place until March next year but, if Corbyn is elected leader, he will find himself up against Cameron in the Commons within days. The new Labour leader is due to address the TUC conference on the Tuesday after the result is announced, and Corbyn would probably receive a joyous reception. But prime minister’s questions takes place the following day, and Corbyn would have to face the prime minister knowing that, even if Labour MPs can summon up the enthusiasm to cheer him, for the vast majority who did not back his leadership bid, their support will not be sincere.

Later this autumn Cameron may ask MPs to vote to back air strikes against Islamic State in Syria. The issue has the potential to split a Corbyn-led Labour party, but the Tories are divided on this issue too, and Cameron would be extremely wary of anything that suggested he was trying to manipulate this for party political purposes.

Trident is different because Labour’s opposition to nuclear weapons in the 1980s was one of the factors credited with making the party unelectable during the Thatcher years. Osborne can take comfort in the knowledge that support for unilateralism is still a minority pursuit in the UK, with one recent YouGov poll showing only 20% of voters favoured giving up nuclear weapons.



Osborne announces £500m for Faslane and says Corbyn threatens UK security Read more

But the issue may not have quite the salience that it did in the 1980s. Most voters do not cite Trident as a key concern and polls show that, apart from those who want Britain to give up nuclear arms completely, the rest are fairly evenly split over whether to renew Trident with an expensive, like-for-like system, which is what the government wants, or opt instead for a cheaper, watered-down version.

Intriguingly, in his memoirs, Tony Blair admitted the case for getting rid of Trident was respectable. “The expense is huge, and the utility in a post-cold-war world is less in terms of deterrence, and non-existent in terms of military use,” the former Labour prime minister said. But on balance he decided getting rid of it was too big a risk.

In Scotland, voters are much more hostile to Trident, with some surveys showing almost half the population wanting Britain to abandon the nuclear deterrent, making Corbyn’s stance much less risky for Labour there than in the UK as a whole.

This could have an effect in the Scottish parliament elections next year. But Osborne is more focused on 2020, when he would like to be the Conservative leader facing Labour.