The threat of a recession-driven 10 per cent cut in the defence budget next year has raised more doubts over whether Britain can afford to spend £20 billion on replacing the Trident nuclear deterrent.

The Ministry of Defence’s big equipment projects are going to be re-examined in a review after the next general election, whoever is in power, with the Conservatives talking about possible 10 per cent cuts across Whitehall.

The renewed debate on the Trident replacement programme was started this week by Nick Clegg, the Liberal Democrat leader, who said that his party would scrap the proposal to maintain Britain’s deterrent with a “like-for-like” ballistic missile submarine system.

Lord Robertson of Port Ellen, a former Labour Defence Secretary and Nato Secretary-General, said that it was important for the Trident replacement programme to be included in a defence review.

“I’m not saying it should be scrapped, far from it,” he said. “If it was, no one seems to have taken into account the huge cost of decommissioning the submarines. But there is room for operating the current submarines for longer, and the defence review needs to look at that.”

If work on the next deterrent submarine force could be delayed by a few years, progress might by then have been made in reducing American and Russian nuclear stockpiles significantly, and Britain could participate in a multilateral disarmament programme, he said.

The replacement Trident programme is at an early stage and little money has been spent. BAE Systems, the Royal Navy and the MoD are working together on designs for the new submarine. The Navy insists that the first of the new submarines must be ready to enter service in 2024.

Despite Lord Robertson’s suggestion of extending the life of the existing Vanguard-class boats, navy sources said that their hulls could not be kept in service any longer. Their lifespan has already been “stretched” from 2019 to 2024 to ensure there was no break in the deterrent patrol cycle, the sources said.

Lord Ashdown of Norton-sub-Hamdon, the former Liberal Democrat leader, said that the MoD was already facing a £10 billion budget deficit next year, and that the Trident replacement programme should be abandoned.

“I see no circumstances to renew Trident. There is a massive hole in the defence budget — a shortfall of around £10 billion within the £36 billion budget — we can’t even pay for what we’ve got,” he said.

The Royal Navy’s other big equipment programme — the two 65,000-tonne aircraft carriers, costing £3.9 billion — will also be included in the defence review. But by the end of this year, £1 billion will have been spent on the project, and the steel-cutting of the first ship is due to take place next month.

Admiral Lord Boyce, who retired as Chief of the Defence Staff in 2003, told The Times that if a future government decided to scrap the Trident replacement, the Navy’s current four Vanguard-class submarines should be recalled immediately.

“My personal view is that if the Government were to decide not to have a deterrent in the future, then it should order the Trident submarines home,” he said. “All Trident operations should stop. You can’t have a government announcing the end of the deterrent from 2024 but still maintain the Trident patrols until the end of their service. Once such a decision is made not to replace Trident, it will undermine the raison d’être of the Trident crews.”

James Arbuthnot, the Tory chairman of the Commons Defence Committee, said that although MPs had delivered three recent reports on Trident, given the state of the MoD’s finances the committee might have to reopen its inquiry into the submarines before the end of this Parliament.

The military is split over the issue. Field Marshal Lord Bramall, another former chief of defence staff, has made it clear that he is against replacing Trident. Other former army chiefs also oppose the £20 billion programme.

However, John Hutton, who resigned as Defence Secretary this month, said: “Not to renew Trident is an incredibly short-sighted view. To do so would be to say that we are unilaterally going to disarm ourselves. What would Britain gain from that? Absolutely nothing.”

Lord Boyce warned: “What you can’t do is make a decision to end the deterrent and then in ten years’ time say it was a mistake and try to reinstate it. The continuity will have been lost and the expertise of operating these submarines will have gone. You can’t cold-start it several years later.”

Sir John Nott, a Defence Secretary in the Thatcher Government, said: “It would be a catastrophe if Trident were no longer continued. It is fundamental to Britain’s defences.”

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