Step-by-step, British politics is being reconfigured. Despite our first past the post system neither of the traditionally dominant parties can be sure of a parliamentary majority in May, and smaller parties are now stepping to the fore as potential power-brokers. The most interesting recent development is the coming out of the anti-austerity troika – SNP, Plaid Cymru and the Green Party. They are all already Westminster parties, and the SNP at least has very real prospects of massively increasing on its current six MPs – estimates based on public polling suggest as many as 20 to 40 in total. They would together be willing to sustain a minority Labour government in power: but with clear conditions. This would be a deal which would push Labour to the left. An anti-cuts agenda is one element of this, but opposition to nuclear weapons is a deal-breaker too: Trident is becoming increasingly significant in British politics.

Clearly Trident was a big factor in the Scottish independence debates. Britain’s nuclear weapons-carrying submarines are berthed at Faslane naval base on the west coast of Scotland and the warheads are stored nearby at Coulport. The determination to eject Trident from Scottish waters was a strong motivating factor in the independence campaign, but the majority of No voters also want rid of it. Scottish Labour has longstanding anti-nuclear policy too, which new Scottish Labour leader Jim Murphy is clearly at odds with – he is adamantly pro-nuclear, which will pose a difficult challenge for Scottish Labour at the ballot box in May.

But Trident is not just a Scottish issue. A very real policy decision on this, which affects us all, north and south of the border, is due in the next parliament. In 2016, a decision on whether or not to replace Trident will be taken. The timing is driven by the rapidly approaching use-by date of the existing system. This means – according to the industry – that to get new subs up and running in time, a decision to start cutting the metal must be made in 2016.

In this context, the anti-Trident demand of the SNP, Plaid Cymru and Greens assumes urgent relevance. Far from being an abstract principle-based demand – although principles are a factor – it is something the next government will concretely need to address. And herein lies the problem for Labour: the Blair government led the charge in 2007 to get parliamentary approval to begin the concept and design work on Trident replacement and despite strong opposition to Trident inside the party, and majority opposition outside, the Labour leadership remains committed to what it quaintly continues to describe as "a minimum credible independent nuclear deterrent".

However, it would be wrong to assume there has been absolutely no movement in Labour’s position. Given the very different strategic security situation in which we find ourselves, over two decades since the end of the Cold War for which these weapons were designed, it would be pretty odd if they hadn’t. Recent policy suggests some room for keeping their options open: in the event of a Labour government, Trident will be included in the next Strategic Defence and Security Review. That may not sound like much, but in fact the last Review, under the coalition government in 2010, just assumed Trident would be replaced without any examination, even though the same government’s National Security Strategy – published simultaneously – actually downgraded the threat of state-on-state nuclear attack. Given the general view that nuclear weapons have no military use whatsoever, a thoroughgoing strategic assessment would seem like the minimum that should be required.

Apart from the obvious common sense of getting rid of a redundant Cold War relic, a decision not to replace Trident would deliver more than the backing to form a government. It could provide the wherewithal to balance the books: for a government committed to paying down the deficit, a decision not to spend over £100bn on nuclear weapons has got to be a runner. But whatever the reason, now’s the time for Labour to urgently rethink Trident.