Nearly half of the 22 serious fires since 1987 were on submarines that could have been carrying nuclear weapons. At least seven occurred when the boats were in Scottish ports.

Details of the fires have not been revealed before, and critics said incidents were much more frequent than they realised. Deaths have already been caused, and a major blaze could spark an environmental catastrophe, they say.

The SNP defence spokesperson at Westminster, Angus Robertson MP, said the fires were “very disturbing”. Their seriousness “cannot be brushed under the carpet”, he told the Sunday Herald.

“It … raises some very inconvenient questions for the prime minister as he plans to spend billions on a new ­generation of Trident submarines.”

MoD figures show there have been a total of 235 fires on nuclear submarines since 1987, with causes including ­electrical faults and deep-fat friers.

The majority – 213 – were classified as “small-scale”, meaning they were localised and extinguished using “minimal onboard resources”. But the remaining 22 fires were more serious.

Three were “large-scale”, ­including one on a Polaris submarine on the Clyde in 1992 that needed help from land-based fire crews to tackle. Nineteen were defined by the MoD as “medium-scale” because they required “significant onboard resources”.

The most recent medium-scale fire, aboard HMS Tireless on patrol under Arctic ice in 2007, killed two sailors. The cause, an explosion in an oxygen ­generator, was blamed on “systematic failings” by the MoD’s board of inquiry.

Few details are available for other serious fires, but they show nine occurred on submarines capable of carrying nuclear missiles. Five happened at the Faslane or Coulport naval bases on the Firth of Clyde, and two at the Rosyth naval dockyard on the Firth of Forth. Six fires broke out on submarines at sea.

Twenty-five submarines have been deployed for periods since 1987, though most are now out of service.

Independent nuclear consultant John Large said: “Though it’s not very likely, a fire involving the solid fuel propellent of Trident missiles would be absolutely disastrous.”

John Ainslie, the co-ordinator of the Scottish Campaign for Nuclear Disarmament, said fires were happening too often. “A major inferno could engulf the Trident missiles or the nuclear reactor, with disastrous consequences.”

According to Ainslie, the potential scale of the problem had been revealed by documents released by the MoD under freedom of information law. Official estimates suggested a three-hour fire in a submarine missile compartment could trigger an accidental detonation, known as a “cook-off”.

The Ministry of Defence, however, defended its safety record as one of the world’s best. “The Royal Navy would not put a submarine to sea unless it was safe to do so,” said a spokeswoman.

She stressed nuclear safety had the highest priority and was ensured through a wide range of measures taking account of scenarios including fire. She added: “The safety record of British nuclear-powered submarines is excellent and there has never been a nuclear accident in the 40 years since they have been in service. As a result of the measures we have put in place, the likelihood of such an accident is extremely remote.”