A decision against renewal would be irrevocable, they said in a letter to The Times, adding that the submarines would have to stop patrolling the seas straight away in that case as credibility in the system would be lost. They said the UK has made a huge contribution to nuclear disarmament but warned against compromising Britains security in what they described as an uncertain world. In an uncertain world where some powers are now displaying a worrying faith in nuclear weapons as an instrument of policy and influence, it would be irresponsible folly to abandon Britains own independent deterrent, reads the letter signed by 20 people including former GCHQ director Sir David Omand and former head of the Royal Navy Admiral Sir Jonathon Band. Trident is a system of submarine-based nuclear missiles, based on four boats. At any time at least one of them is at sea, on patrol, somewhere in the world. It is operated by the Royal Navy and based at the Clyde Naval Base on the west coast of Scotland. The name Trident comes from the American-built UGM-133 Trident II missiles which are carried by the boats. A House of Commons Library note suggests that in 2013\/14 prices, replacing the whole Trident system would cost about £17.5 billion to £23.4 billion. Yesterday Defence Secretary Michael Fallon refused to confirm the Conservatives would vote with a minority Labour government to renew Trident. The SNP, Greens and Plaid Cymru are in favour of scrapping Trident, in contrast to the Labour and Conservative position.