Private firms working at Clyde nuclear bases are being given a multi-million pound get-out by Westminster so they will not have to pay compensation or clean-up costs after "potentially catastrophic" accidents.

The Ministry of Defence plans to sign deals with contractors at Faslane and Coulport that limit their financial liability in case of injuries, deaths, explosions, fires and radiation leaks to no more than £100,000. The vast majority of costs, which could run into many millions of pounds, will be met by taxpayers.

The revelation has shocked politicians, experts and campaigners. Labour MP Paul Flynn, who has lodged a motion in the House of Commons opposing the move, said: "Commerce reaps the profits and the public purse is looted to pay immeasurable costs."

Faslane, near Helensburgh, is home to the UK's four nuclear submarines armed with Trident nuclear missiles, and a fleet of nuclear-powered, conventionally armed subs. 200 nuclear warheads are kept Coulport on nearby Loch Long. Both have a chequered safety record.

Defence Minister Andrew Murrison said the Treasury has agreed to relieve contractors of the liability for accidents, otherwise the contracts would become "untenable".

Documents presented to MPs say the MoD has already restricted the liability of engineering giant Babcock, which manages the bases, to £100,000 "per nuclear event".

"The purpose of the indemnity is not to absolve contractors of their responsibilities, but to ensure the MoD can employ contractors," said an MoD spokeswoman. She said the measure was "common practice".