What is Trident? The debate over the U.K.'s nuclear deterrent

Alice Foster, Express
16 February 2016
What is Trident?
Trident is Britain's only nuclear weapon system and consists of four submarines carrying missiles and warheads.
Controlled by the Royal Navy from a Scottish base, at least one submarine is always on patrol in a bid to deter nuclear attacks.
Trident is the most powerful but also the most expensive capability in the British military arsenal.
When was Trident created?
In 1980 the Thatcher government announced plans to introduce Trident to replace the UK's previous Polaris missile system.
The development of Trident took place amid heightened tensions during the Cold War. Trident was first brought into use in 1994.
Why does Trident need to be replaced?
The current fleet of submarines is set to reach the end of its working life in the late 2020s.
No decision has been taken on whether to replace Trident, but work has already started on a possible replacement.
The replacement of Trident will cost more than £100 billion, according to the Campaign for Nuclear Disarmament.
What are political views on Trident?
The Conservative government supports the renewal of Trident – its replacement was a key part of the party's manifesto.
Prime Minister David Cameron has argued that the UK would be "foolish" to give up its ultimate weapon of defence amid ongoing nuclear threats.
The SNP opposes the renewal of Trident, while the Liberal Democrats argue that it is a relic of the cold war and there are better ways to keep the UK safe.
Does Labour want to replace Trident?
The Labour party is engulfed in a bitter row over the issue and is carrying out a defence review into its policy on Trident.
Jeremy Corbyn opposes Trident and pledged to get rid of nuclear weapons entirely during his Labour leadership campaign last year.
But before his election, Labour had supported the renewal of Trident and saw it as a "cornerstone" of peace and security for Britain.