MPs will engage in a six-hour debate over the future of the UK's nuclear deterrent from this afternoon (18 July 2016). The row over the renewal of Trident will come to a head when a vote is held in the House of Commons around 10pm BST.

Britain's new Prime Minister Theresa May is expected to open proceedings, with a defence of the continuous at-sea programme. The Conservative premier will claim it would be an irresponsibility to scrap the system, which cost £18.35bn ($24.31bn, €22bn) to create and will cost at least a further £41bn to upgrade over its 20-year lifetime.

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The government's pro-Trident position is clear, but the Labour opposition is split three ways over the issue.

Long-time unilateralist Jeremy Corbyn is expected to vote against renewing the programme, while shadow foreign secretary Emily Thornberry is hoping that Labour MPs abstain on the vote and some backbenchers are backing Trident.

Barrow and Furness MP John Woodcock claimed that his party's official policy is to back the renewal of trident.

Unite and GMB, Labour supporting trade unions, also take this pro-Trident stance since thousands of their members would face job uncertainty if it were ditched.

Thornberry, the former defence secretary, had led a policy review into Labour's military positions. But the report, originally planned for a week after the EU referendum, has been delayed because of the Brexit result.

The SNP, the third-largest part in the Commons behind the Tories and Labour, are unambiguous on the issue. The nationalists oppose renewing the nuclear weapons programme. Angus Robertson, the SNP leader at Westminster, has branded the system as "immoral, obscene and redundant".

The debate on Trident's renewal is expected to take place between 4pm and 10pm in the main Commons' chamber. You can watch the event live on Parliament TV and BBC Parliament and follow @IBTimesUK for updates.

What the Trident nuclear deterrent is and why it matters to UK security?

Trident operates a continuous at-sea nuclear deterrent. That means one of the programme's four nuclear submarines, which are based in the Faslane area of Scotland and operated by the Royal Navy, is always on patrol.

These Vanguard-class submarines are around 491ft in length, or more than twice the size of two Boeing 747s, and powered by steam. A nuclear reactor inside the underwater vessels boils sea water, the steam from which is then used to propel them.

The four submarines – HMS Vanguard, HMS Vengeance, HMS Victorious and HMS Vigilant – are capable of carrying 16 Trident II D5 ballistic missiles, produced by the American arms manufacturer Lockheed Martin, each armed with up to eight nuclear warheads. As it stands, each submarine only carries three Trident missiles.

Their power and precision is stunning. Each missile is 44ft long, 83 inches in diameter, capable of exceeding speeds of more than 13,000mph, and can hit targets up to 7,000 miles away, accurate to within a few feet. Read more here.

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