SNP defence spokesman Stewart McDonald said the UK had become an “irresponsible” nuclear power, and claimed the nuclear deterrent is a “big-willy gesture of a small-willy nation”.

McDonald hit out during a Commons debate to mark 50 years of the UK’s continuous at-sea nuclear deterrent. In a division forced by the SNP, not a single Scottish Labour MP voted against nuclear weapons, despite non-renewal of Trident being the policy of Richard Leonard’s party.

McDonald accused Jeremy Corbyn of “selling out” for failing to oppose the Tory government.

“As a long-standing opponent of weapons of mass destruction, Jeremy Corbyn has sold out his own principles by sitting on his hands and failing to walk through the voting lobby with the SNP to oppose this outdated and immoral vanity project,” he said.

The motion celebrating Britain’s nukes was passed by 241 to 33 – with most of the Labour Party abstaining.

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Defence Secretary Gavin Williamson had opened the debate, saying “half a century ago HMS Resolution glided into the Clyde and sailed into the history books” as the first submarine to take part in the mission.

Addressing those who no longer think the UK should have a continuous at-sea presence, he said those who believe it “is simply a Cold War relic” should be reminded that the “the nuclear dangers have not gone away”, saying the “geopolitical situation is more unstable than ever before”.

And Labour agreed – with shadow defence secretary Nia Griffith confirming that Labour is committed to the renewal of Britain’s nuclear submarines.

She said: “The threats facing the UK are real and undiminished. There is a need to deter against the use of nuclear weapons in all circumstances. None of us ever wants to be in a position where the deterrent is used.

“If we ever got to that situation, it would represent a catastrophic failure of our rules-based system and the very concept of deterrence.”

During the summing up of the debate by Labour’s shadow defence minister Wayne David, the SNP were quick to point out that Richard Leonard’s branch office in Scotland are supposed to be opposed to Trident renewal.

“The position of the Scottish Labour Party is the same as the Scottish National Party,” said McDonald. “Can you explain why they’re wrong, and he’s right?”

READ MORE: Strict timetable for getting rid of Trident after independence on SNP agenda

David replied: “I have no doubts whatsoever that this is not a devolved matter. The policy which counts is the policy of the British Labour Party.”

McDonald said that anybody who thought celebrating nuclear weapons in the current time was a good use of House of Commons time was “off their head”.

He said: “Only in this House of Commons, at this time against the backdrop of a major constitutional crisis where each day is worse than the last could it be thought of as a good use of time to back-slap each other on the UK being 50 years as a marine nuclear power.

“Anyone who thinks that is a good use of our time right now, frankly, is off their head.”

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McDonald said it is “no surprise” that MPs want to “hark on these symbols of power” at a time where the Prime Minister has “the begging bowl” out in the EU.

He added that there is no military or economic case for a continuous at-sea deterrent, and insisted that the UK had become an “irresponsible” nuclear power.