Anti-nuke activists demanded an immediate suspension of Britain's nuclear submarine patrol yesterday after MPs heard of a radiation leak - over two years after the fact.

Defence Secretary Philip Hammond sought to "reassure" the Commons yesterday after admitting that engineers detected radiation spilling into the reactor coolant of the Trident fleet's Vanguard vessel in January 2012.

"These low levels of radioactivity are a normal product of a nuclear reaction that takes place within the fuel but they would not normally enter the cooling water," he said.