The Ministry of Defence says it has absolute confidence in Britain's nuclear weapons system, after reports of a missile test failure.
The Sunday Times says it has been told that the launch of an unarmed Trident II D5 missile from the Royal Navy's HMS Vengeance (pictured above) off the coast of Florida in June 2016 malfunctioned.
The newspaper reports that the missile headed towards the United States instead of a target off the coast of Africa.
The MoD says a test did take place last June, but would not give any further details about any failure.
The incident came ahead of a crucial vote in the House of Commons in July on the renewal of the nuclear weapons system.
Prime Minister Theresa May has refused to say whether she knew about any failed test ahead of the vote.
Mrs May did not mention the test in her speech, in which she urged MPs to back renewal, leading to allegations the alleged malfunction has been covered up.
Labour leader Jeremy Corbyn questioned why no information had been given about this test before July's vote in the Commons. He said:
"We understand the Prime Minister chose not to inform Parliament about this and it's come out through the media some months later. It's a pretty catastrophic error when a missile goes in the wrong direction and whilst it wasn't armed, goodness knows what the consequence of that could have been. I think we need a serious discussion about that."
In response to the claims about the test failure, a Government spokesman said:
"The capability and effectiveness of the Trident missile, should we ever need to employ it, is unquestionable. In June the Royal Navy conducted a routine unarmed Trident missile test launch from HMS Vengeance, as part of an operation which is designed to certify the submarine and its crew.
"Vengeance and her crew were successfully tested and certified, allowing Vengeance to return into service. We have absolute confidence in our independent nuclear deterrent."
"We do not provide further details on submarine operations for obvious national security reasons."