Leading article: There is a strong case for not renewing Trident

Some of the liveliest exchanges in the first two leaders' election debates concerned the future of the Trident nuclear deterrent.

Nick Clegg argued the Liberal Democrat position that Trident was designed for a cold war scenario that no longer obtained and that it should be possible to find a "cheaper and better" alternative. He was taken to task by both Gordon Brown and David Cameron who accused him of flirting with unilateral nuclear disarmament and putting Britain's security at risk.

In fact, Mr Clegg stopped short of proposing that nuclear deterrence be abandoned completely. What he called for, as a first step, was the inclusion of Trident in the strategic defence review that is to be conducted after the election, whoever wins. But that is the barest minimum of what is required.

Of course, Trident must be included in the defence review. The renewal decision was taken by Tony Blair in 2007, with only the most summary of parliamentary debate, and endorsed by Mr Brown when he became Prime Minister. This is the rationale for leaving it out. But it is absurd to review Britain's future defence needs, while omitting by far the biggest, most symbolic and most expensive item.

That the renewal of Trident is a live issue was illustrated earlier this week when the former Chief of Defence Staff, Lord Guthrie, joined other retired top brass in calling into question the need for a direct replacement of Trident. If there are senior military people who believe times have changed, there is at very least a real discussion to be had.

For our part, we find much more to be gained than lost in reconsidering the renewal of Trident. Cost is an issue, but so is the signal that renewal sends about UK intentions. Mr Cameron is right that "you can't rustle up a nuclear deterrent at the last minute". But nor can you exchange one that proves unsuited to new requirements. Our future defences must be considered broadly, as an integrated whole. Seen in that way, renewing Trident is in every sense a luxury Britain cannot afford.