On 25 September, the next leader of the Labour Party will be announced. This is the person Labour believes should hold the keys to Britain's nuclear arsenal.

Yet, despite one of the longest leadership campaigns in memory, there has been no detailed debate about the role and scale of Trident, Britain's continuous at-sea nuclear deterrent.

The clearest positions have been adopted by Diane Abbott, who supports unilateral nuclear disarmament, and David Miliband, who argues that a full renewal of Trident is the only minimal deterrent option Britain has.

To many Labour observers, David Miliband's views represent the head and Abbott's the heart of their party's attitude to nuclear deterrence -- that Britain gets behind Trident or gets out of the nuclear game.

This is a missed opportunity, as a growing number of military experts are voicing scepticism about the current cost and strategic benefit of a defence system designed for the cold war era.

In July, the leading military think tank Rusi published the excellent report Continuous at Sea Deterrence: Costs and Alternatives (PDF). Written by Professor Malcolm Chalmers, one of Britain's foremost nuclear experts, the report lays out four clear options short of full renewal.

According to Chalmers, simply delaying the decision to renew fully for another five years could save as much as £5bn over the next decade. This at a time of severe government debt. Other options considered, such as reducing the number of submarines, could make even more savings while maintaining an appropriate deterrent.

In response to claims that anything less than the immediate renewal of Trident endangers Britain's ability to retaliate to a nuclear attack, Chalmers says it is a matter of "balancing the risk".

He makes the case that Britain's nuclear response is at present maintained in anticipation of a massive surprise attack, which could destroy that response outright. By contrast, the rest of Britain's armed forces are designed on the assumption that the UK would have a long warning period of threat to its homeland. This has allowed conventional forces to be designed primarily to fight expeditionary wars abroad.

Chalmers argues that if a cold-war-type threat to the UK re-emerged in the next 20 or 30 years, then Britain could re-equip as that threat began to loom on the horizon.

The failure to discuss the full range of options on Trident renewal properly suggests Labour leadership candidates are still defined by the battles of the 1980s. Eric Joyce MP, a former PPS to the defence secretary, has observed that Labour's "strict nuclear line" comes from the perception that advocating unilateral disarmament was a key failing in Labour's 1983 manifesto -- nicknamed the "longest suicide note in history".

Since then, Britain's nuclear deterrent has become a shibboleth for those in the party to define themselves against.

But it is easy to overemphasise the importance of this policy to Labour's wilderness years. Given issues such as the Falklands victory, the split that led to the creation of the Social Democratic Party and the miners' strikes, the role of nuclear disarmament in losing Labour elections was perhaps more emblematic than critical. When the policy was dropped after the 1987 defeat, Labour appeared no more electable for it in 1992.

It is also important to remember that Labour in the 1980s was not simply made up of a unilateral disarmament left and a pro-nuclear right. A third way was followed by a group of more than 60 Labour MPs who supported the European Nuclear Disarmament Campaign (END).

While END never captured the public consciousness in the manner of CND, it successfully built a broad coalition of unions, politicians and civil society groups across the continent in favour of a European nuclear-free zone "from Poland to Portugal" (PDF). The main focus was to rid Europe of short-range "battlefield" or tactical nuclear weapons, which were seen as increasing the chances of a nuclear exchange.

This was a multilateralist, pragmatic disarmament movement, mainly supported by left-leaning Labour MPs, such as Robin Cook. It could claim a tangible success in putting pressure on the superpowers for the eventual withdrawal of tactical nuclear weapons by the end of the 1980s from Europe.

Such a third way is missing from the debate, which is still split between backing a maximal deterrent or unilateral disarmament. There is an opportunity for Labour's next leader to support a cost-effective, credible nuclear weapons system, built to protect against the threats of today, not the ghosts of the past.

Alex Holland is a Labour councillor for Brixton Hill, Lambeth