The strategic defence and security review set up by the government will be "skewed" unless it includes the future of the Trident missile system, a former Liberal Democrat leader and spokesman on defence and foreign affairs said today.

Sir Menzies Campbell said: "Maybe it's the shape of the missiles but every time Trident is mentioned there is an outbreak of priapism on the Tory backbenchers. There is a real risk that the whole strategic defence review will be skewed because of the obsession with Trident. It makes no sense whatsoever to exclude Trident, the strategic deterrent, from a proper strategic review."

The government says Trident must be excluded from the review, though its value for money could be scrutinised. The coalition agreement says the Lib Dems may "continue to make the case for alternatives".

Liam Fox, the defence secretary, is now embroiled in a row with the Treasury, which wants the capital costs of a new Trident system to come out of the defence budget and not from a separate account as the government, like its predecessor, promised.

The chiefs of staff publicly sidestep questions about Britain's nuclear weapons, saying they are a political matter. Navy chiefs, including Sir Mark Stanhope, the first sea lord, have made clear their view is that if the UK is to have nuclear weapons, only a like-for-like Trident replacement would be an effective "deterrent". Army chiefs, including General Sir David Richards, who will become chief of the defence staff in October, are more sceptical about Trident's worth.

The capital cost of replacing the existing Trident fleet with four new nuclear ballistic missile submarines is officially estimated at £20bn. Running costs in coming decades could more than double that figure.

Better value from money spent on the existing Trident fleet could be got by extending its life and co-operating on patrols more closely with the French, Campbell said. Authoritative research showed the life of the existing fleet could be extended.

He also challenged the government to publish the results of the promised "value for money" audit on Trident. Fox last week described the capital costs of a successor to Trident as "pretty good value".

Nick Harvey, the Lib Dem defence spokesman during the election campaign, who is now armed forces minister, said in April: "Omitting the single largest procurement project from the strategic defence review makes a complete mockery of the whole exercise."

The Lib Dems said during the election that the need for "continuous at sea deterrence" no longer existed. Ending the practice – which ensures one submarine is always on patrol – could extend the life of the four Trident boats well beyond 2024, according to a report by Nick Ritchie and Paul Ingram published by the Royal United Services Institute. These measures could save more than £11bn, they say.