Downing Street has been accused of covering up a Trident missile malfunction weeks before a crucial Commons vote on the future of the submarine-based missile system.

The Sunday Times reports that a Trident II D5 missile test ended in failure after it was launched from the British submarine HMS Vengeance off the coast of Florida in June last year.

The newspaper reports that the cause of the failure remains top secret, but quotes a senior naval source saying the missile, which was unarmed for the test, suffered an in-flight malfunction after launch.

It was reportedly intended to be fired 5,600 miles to a sea target off the west coast of Africa but may have veered off towards America instead.

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The source told the newspaper: “There was a major panic at the highest level of government and the military after the first test of our nuclear deterrent in four years ended in disastrous failure.

“Ultimately Downing Street decided to cover up the failed test. If the information was made public, they knew how damaging it would be to the credibility of our nuclear deterrent.

“The upcoming Trident vote made it all the more sensitive.”

In July, MPs voted by 472 to 117 to back the renewal of Britain's Trident nuclear deterrence. The overwhelming vote supported the Government's plans to spend up to £40 billion on four new Successor-class submarines.

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Labour former defence minister Kevan Jones has demanded an inquiry into the failed test.

“The UK’s independent nuclear deterrent is a vital cornerstone for the nation’s defence,” he told the newspaper.

“If there are problems, they should not have been covered up in this ham-fisted way. Ministers should come clean if there are problems and there should be an urgent inquiry into what happened.”

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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.