THERESA May was last night urged to postpone a long-awaited Commons vote on the renewal of Trident amid the “unprecedented turmoil” of Brexit, and to tell MPs its true cost.

SNP Westminster leader Angus Robertson warned the Prime Minister she would start her premiership on the wrong note if she pushed ahead with tomorrow’s vote.

It was too important to rush through parliament after a month of “back-stabbing, score settling and navel-gazing” among the Conservatives and Labour, he said.

Robertson also said that, whenever the vote came, MPs must know the full 30-year lifetime costs of maintaining the UK’s nuclear deterrent.

The current estimate of £167bn was based on “partial information”, he said, and the Campaign for Nuclear Disarmament had put the true figure at £205bn.

The timing of tomorrow’s vote was decided last week by David Cameron, while he was still expecting to stay on as Prime Minister until September.

However, May has also backed a vote before the summer recess begins on Thursday, saying it would be “sheer madness” to give up the deterrent given the many security threats facing the UK.

Trident has three main elements - four Vanguard class submarines based at Faslane on the Clyde, which provide a continuous at-sea deterrent, Trident II D5 Ballistic missiles leased from the US, and nuclear warheads, stored eight miles from Faslane at Coulport.

The Commons voted 409-61 in principle to maintain Trident beyond its current service life in 2007, paving the way for £3bn of design work on new submarines.

The last coalition government promised MPs would also have a vote on “main gate” - the point-of-no-return decision to invest and proceed to manufacture with the new subs.

However the new Tory government dropped its plan for a definitive main gate decision in December, and tomorrow’s vote will be another on the general principle of a nuclear deterrent using four Successor class submarines.

With a Conservative majority in the Commons and UK Labour still having the deterrent as its policy, despite Jeremy Corbyn’s lifelong opposition to nuclear weapons, the vote is virtually guaranteed to pass, despite the opposition of almost every Scottish MP.

Robertson said: “Trident is an immoral, obscene and redundant weapons system.

“Over the last few weeks we have witnessed unprecedented political turmoil, as the entire Westminster system was shown to be completely unprepared for the prospect of a Brexit vote.

“Having spent the best part of a month engaged in backstabbing, score-settling and navel-gazing, neither the Tories nor Labour are in any fit state to be giving proper scrutiny to decisions as important as this.”

In a joint statement last week, eight Catholic bishops in Scotland urged the UK Government to take “decisive and courageous steps” towards disarmament, and said “lives are being lost now because money that could be spent on the needy and the poor is tied up in nuclear arsenals”.

The Church of Scotland also said it would be “morally and economically indefensible” to spend hundreds of billions on weapons of mass destruction, especially when services were being cut.

Robertson added: “Theresa May has make big commitments about a new style of government. I would urge her to put her words into action by showing that the Tories’ political games around Trident are a thing of the past – and allow MPs, and the public, the fully informed debate that they deserve.”

A UK government insider said: “The SNP’s call for delay is a bit rich given this has been debated for years, not least 18 months ago when the SNP led and lost a vote in the Commons.”