Labour will not reverse its decision to keep Britain's Trident nuclear deterrent, the shadow defence secretary has said.

Nia Griffith stressed it was party policy to support the nuclear deterrent, adding uncertainty in the world meant this is not the time to be "descaling" it.

Labour leader Jeremy Corbyn voted against Trident renewal in July 2016.

The Commons vote saw MPs back the replacement of the existing submarine fleet carrying the missiles with four new Successor submarines.

Renewal of the submarines for the continuous-at-sea deterrent has been predicted to cost £31 billion, with a £10 billion contingency fund also set aside.

Ms Griffith told BBC One's The Andrew Marr Show: "It's Labour Party policy that we keep Trident.

"The decisions have been taken, the work is being undertaken and that is not a decision we're going back on.

"So we're very, very clear - having a nuclear deterrent is a very important part of our defence policy. It's also an important part of being a tier-one nation and being in the UN Security Council."

Asked about her previous remarks in which she questioned the need for Trident, Ms Griffith said: "I think if you look at the world today it's a more uncertain place than it's ever been.

"I think if you look at the way the United States is not stepping up to the mark, I don't think this is the right time to be getting rid of our nuclear deterrent.

"Of course we need to keep an eye on costs, of course we need to make sure we get value for money, and it is a challenging situation when it's a single-source purchase - much more difficult than when you have competition.

"But at the end of the day, this is not the time to be descaling our nuclear deterrent."

Ms Griffith later said she would "absolutely" support sending more British troops to Afghanistan.

Last month, Defence Secretary Gavin Williamson was understood to have written to Prime Minister Theresa May recommending that the UK increased its numbers to bolster efforts to counter the Taliban.

It was said between 400 to 450 soldiers could be sent to join the roughly 600 already deployed in non-combat roles following pressure from US President Donald Trump for international allies to do more.

Ms Griffith, asked if Labour would support sending more troops to Afghanistan, said: "We certainly support the idea that you cannot abandon a process halfway through.

"We know it's not going to take one year or two years, it's going to be 20, 30 years for the government of Afghanistan to become stable and as stable as we would like - so it will take longer.

"And if we have the expertise that we can offer, then certainly we're willing to put that in."

Pressed again if she would support putting more British troops into Afghanistan, Ms Griffith replied: "Absolutely."