DEFENCE of the realm is, we are often told, the first duty of any government and few issues raise as much passion as that of whether to retain Britain’s nuclear deterrent.

Policy presentation is easier for those parties which have a clear-cut, unified approach on the subject.

The Conservatives want to keep the continuous-at-sea deterrent, involving four nuclear submarines. The SNP wants to scrap it, believing it to be costly and immoral.

For Labour, however, the issue is not so straightforward, which has already been illustrated during the election campaign.

The official UK party policy is to maintain and renew the nuclear deterrent. But Jeremy Corbyn, a vice-president of CND, has made clear that if he became Prime Minister, he would never press the button, and he has insisted the party is committed to “no first use”.

This has opened Labour up to attack from its opponents. They argue the point of a deterrent is to deter but if a potential aggressor knew the UK’s leader was not prepared to use nuclear weapons in a first use or retaliatory strike, then they would cease to be a deterrent.

Moreover, Scottish Labour is opposed to retaining Trident, which on the campaign trail in Scotland can prove problematic as one part of the party supports the nuclear deterrent and another opposes it. To complicate matters further, Kezia Dugdale, the party leader in Scotland, supports keeping the deterrent.

Last year, the Commons backed the renewal of Trident by 472 votes to 117. Labour split on the issue with 140 of its 230 MPs going against their leader and backing the motion in a free vote.

Earlier this month, Mr Corbyn, explaining his foreign policy at the Chatham House think-tank in London, mentioned how he was often asked if, as Prime Minister, he would press the nuclear button.

“It’s an extraordinary question when you think about it,” he declared. “Would you order the indiscriminate killing of millions of people? Would you risk such extensive contamination of the planet that no life could exist across large parts of the world?”

He used the speech to insist he was not a pacifist but placed clear emphasis on nuclear disarmament and the rule of international law.

At the same event, the Labour leader explained if his party won power, it would initiate a strategic defence review, suggesting the pro-Trident policy would be reconsidered.

Later, Emily Thornberry, the shadow foreign secretary, noting how she was “sceptical” about the nuclear deterrent, was asked if her party’s pro-Trident stance would continue after the review. “No, of course not,” she said. “If you are going to have a review, you have to have a review.”

But Nia Griffith, the shadow defence secretary, contradicted her colleague, noting: “With all due respect, Emily is not the shadow defence secretary, I am.”

The review, she stressed, would be about how to spend the defence budget, saying: “What it is not about is questioning whether we would have a Trident nuclear deterrent because we settled that last year.”

Later on the campaign trail, Mr Corbyn reiterated his party’s policy, as expressed in the manifesto, that Labour was “committed to Trident”.

Conservatives l Retain continuous-at-sea nuclear deterrent as “ultimate guarantee of our security”.

l Spend at least two per cent of GDP on defence, meeting the Nato commitment.

l Increase the defence budget by 0.5 per cent above inflation every year.

l Strengthen legal services rules and restrict legal aid to firms which make vexatious claims against service personnel.

l Invest £178 billion in new military equipment over next decade Labour l Support renewal of Trident.

l Lead multilateral efforts to create “nuclear-free world”.

l Spend two per cent of GDP on defence, meeting Nato commitment.

l Commit to procurement supporting British steel and defence manufacturing industries.

SNP l Oppose Trident renewal; will use £100bn cost to create better education and healthcare.

l Seek to ensure there is proper oversight and parliamentary approval for any future UK military action, which would need to be in accordance with the principles of the UN Charter.

l There should be ocean-going conventional patrol vessels based permanently in Scotland.

l Keep existing conventional bases in Scotland with no further erosion of the Scottish regiments and traditional regiments should be restored.

Liberal Democrats l Maintain a “minimum” nuclear deterrent, procuring three boats not four, and moving to a “medium-readiness responsive posture”.

l Promote European defence integration where appropriate by enhancing European defence industry co-operation.

l Commit to spending two per cent of GDP on defence.

l Invest in the security and intelligence services to counter cyberattacks.

l Support the Armed Forces Covenant and ongoing work to support veterans’ mental health.

Greens.

l Scrap the Trident replacement, saving at least £100bn over the next 30 years.

Ukip l Support Trident renewal.

l Return RAF Kinloss and Leuchars to full operational status.

l Guarantee a job office in the police or prison services for any Scot who has served in the Armed Forces for at least 12 years.

l Introduce a “boots to business” scheme to help with money and advice for any veteran wishing to set up their own firm.

l Ensure fast-track health care for veterans.