Replacing Trident, the U.K.'s nuclear weapons system, will cost "at least" £205 billion ($295 billion), according to the Campaign for Nuclear Disarmament (CND).
In an announcement on Thursday, the CND said that the cost had doubled since 2014. The Trident system is in the Royal Navy's Vanguard Class submarines, which are set to be replaced by four new "Successor" class submarines.
"For too long the pro-Trident lobby has been in denial about the real cost to our economy of Trident replacement," Kate Hudson, general secretary of the CND, said in a statement.
"These new calculations, drawn from actual government figures, show that the bill has spiralled beyond all expectations," Hudson added.
The government describes the replacement plan as equal in scale to huge infrastructure projects such as railway scheme Crossrail, which is projected to cost £14.8 billion.