STEWART Hosie said last night it was an “unthinkable and indefensible sum” to renew Trident after new figures revealed the overall cost could reach £167 billion instead of the £100bn already proposed.

The SNP deputy leader said: “How can Tory MPs expect to be able to look their constituents in the eye when on the one hand they are taking thousands of pounds from hard-working low income families who rely on tax credits and with the other they plan to pour money into brand new weapons of mass destruction?

“It was already ludicrous to consider the renewal of Trident when the cost was £100bn but these figures show just how dangerous the Tories’ obsession with nuclear really is.”

“And at a time when Scotland’s conventional defence capabilities have shrunk dramatically with base closures and less than 10,000 personnel it is alarming that there seems to be endless amounts of money available for abhorrent nuclear weapons.”

Even senior Tories are now raising concerns about wasting the cash while people are struggling under their cuts.

Crispin Blunt, who chairs the Commons foreign affairs committee, said the “excessive” expenditure suggested it was time to pull the plug on the project. He has been told by a defence minister that the cost of the replacement of the ageing submarine fleet – previously put at around £25bn – was “currently being refreshed” as part of the UK Government spending and strategic defence reviews, suggesting it could go higher.

In a Commons written answer, Philip Dunne also confirmed that in-service costs were expected to swallow up six per cent of the defence budget through to the 2060s.

Blunt calculated that, given the Government’s commitment to meet a Nato target of devoting two per cent of national wealth to defence – and assuming annual GDP growth of 2.48 per cent between 2020 and 2060, that would see the bill spiral to £167bn, much higher than previous estimates.

In a statement he said: “How much is too much? There has to be a point where this programme ceases to be value for money.

“I believe that this level of spending commitment is excessive as it will mean forgoing an effective conventional capability in order to maintain one weapons system that is unlikely ever to be used.

“This doesn’t even consider the inherent risk of concentrating our deterrent on one platform that I fear may be very visible to advanced sonar by 2050. If that happens the mistake will be even more costly.” He added that the price was “now too high to be rational or sensible”.

A crunch Commons vote on whether to go ahead with the renewal is due within months.