The overall cost of replacing and maintaining Britain's nuclear deterrent will reach 167 billion pounds ($256 billion), much more than expected, according to a lawmaker's and Reuters' calculations based on official figures.

The Scottish Nationalist Party, which wants Britain's Scotland-based nuclear-armed Trident submarines scrapped, called the sum "unthinkable and indefensible" at a time when deep cuts under the government's "austerity" policies mean "thousands of people across the UK are struggling to afford basics like food".

Some military officials also oppose investment in Trident, saying the money would be better spent on maintaining the army and on more conventional technology, which have also faced cuts.

Until now, Prime Minister David Cameron's government has said replacing the ageing fleet of four submarines which carry nuclear warheads to provide a continuous at-sea deterrent would cost an estimated 15-20 billion pounds.

It has as yet given no official estimate of the cost of its replacement and maintenance.

Critics have previously said Britain will need to spend 100 billion pounds, a figure based on a 2014 report by the independent Trident Commission.

In a written parliamentary response to Crispin Blunt, a lawmaker in Cameron's Conservative party, Minister of State for Defence Procurement Philip Dunne said on Friday the acquisition of four new submarines would cost 25 billion pounds. He added that the in-service costs would be about 6 percent of the annual defense budget over their lifetime. The total defense budget for 2014/15 reached 33.8 billion pounds and rises to 34.1 billion pounds in 2015/16, according to the ministry. "My office's calculation based on an in-service date of 2028 and a missile extension until 2060 ... the total cost is 167 billion pounds," Blunt told Reuters.

The successor Trident program is going to consume more than double the proportion of the defense budget of its predecessor ... The price required, both from the UK taxpayer and our conventional forces, is now too high to be rational or sensible." His figure was based on a presumption that Britain will spend 2 percent of its annual gross domestic product (GDP) on defense, as Cameron's government has promised. READ MORE HERE