The fact that they were useless against international terrorism was no argument for getting rid of them when other countries were acquiring nuclear weapons, he told the House of Commons Select Committee on Defence.
His remarks suggest that the Defence Secretary, like the Prime Minister, has privately decided that the UK will have to start developing a new generation of nuclear weapons in the next few years. He told the MPs it was "highly desirable" but not "essential" that a decision was made before the next general election.
But he added that it was still an open question what form of nuclear deterrent the UK would develop to replace Trident, which is expected to be obsolete by about 2020. The Independent reported yesterday that Ministry of Defence planners were considering replacing Trident with cheaper air-launched missiles.
Speaking to Labour MPs on Monday night, Mr Reid pointed out that within a few years satellites may be capable of detecting submarines at great depths, which would turn Trident into a visible target.
Mr Reid did not say publicly which countries were classed as "potential enemies" - but privately military planners still allow for the long-term possibility that the Russian government will be taken over by aggressive nationalists.
"We have always maintained that so long as some other state that is a potential threat has nuclear weapons, we will retain them. That is the assumption we have at the moment and it is that assumption that we will assess against an analysis of what might be future threats," he told the committee.
"Probably more worrying, some countries have been trying to develop nuclear weapons by deceiving the world, not complying with their obligations under the Non-Proliferation Treaty, for instance in Iran. I think it would be naive to believe that there will be no further proliferation."
Mr Reid admitted that nuclear weapons could notbe used to deter terrorists, but he added: "It is equally true that you can't use special forces to deter a nuclear attack. That does not mean to say that special forces are redundant."
Last night, Mr Reid agreed to hold a private meeting with a group of Labour MPs, to smooth over growing opposition to the prospect of spending billions of pounds on a new generation of nuclear weapons. He was urged to produce a list of tests that would have to be met before Britain committed itself to developing more nuclear weapons, like Gordon Brown's five economic tests that have to be met before joining the euro.
David Chaytor, one of the MPs seeking the meeting, said: "John Reid has himself suggested that there's a large number of questions that have to be answered, such as which countries are likely to be potential enemies. Most Labour MPs would agree that these questions and the responses should be made public."Reuse content