A Trident missile did malfunction last year, a US official has confirmed – as MPs were being told they were not allowed to know the truth.

The rogue missile had to be ordered to “self-destruct” off the Florida coast, the American news channel CNN was told today.

It did not “veer” towards the US – as reported yesterday – the official said, but was diverted into the sea under an automatic procedure when a fault is detected.

To the embarrassment of Defence Secretary Michael Fallon, the report emerged as he was insisting, in the Commons, that no details of the botched test could be revealed.

Both Labour and Conservative MPs accused Sir Michael of a cover-up, demanding to know when he – and then-prime minister David Cameron – were told.

One MP, Labour’s Kevin Brennan, said the secrecy undermined the Commons and was a “don't tell him Pike” strategy, after the Dad’s Army character.

Sir Michael was summoned to the Commons after Theresa May finally admitted she had been aware of the test, but insisted it had been a “successful”.

It was a “demonstration and shakedown” operation undertaken by HMS Vengeance following a refit and both submarine and crew had been “certified” to return to service, No.10 said.

Asked if the Prime Minister was told the missile had veered off course, her official spokeswoman replied: “I don't accept the premise of the question.”

That stance was then echoed by Mr Fallon, who insisted details of tests were never revealed – despite videos of previous successes being posted on YouTube.

But, even as he was speaking, CNN was reporting an explanation given by a “US defence official with direct knowledge of the incident”.

According to the Sunday Times, the missile was meant to be fired 5,600 miles from the coast of Florida to a sea target off the west coast of Africa - but veered towards the US.

However, the US official said the missile was diverted into the sea to self-destruct - an “automatic procedure when missile electronics detect an anomaly”.

Carol Jordan, a senior CNN news editor, tweeted: “A #Trident test did go wrong off the coast of #Florida but the missile self-destructed, a #US defense official has told #CNN”.

In the Commons, Sir Michael continued to state that the test had been “successful” and that decisions on publicity were made "on a case by case basis".

But Shadow Defence Secretary Nia Griffith said: “The British public deserve the facts on a matter as important as Britain's nuclear deterrent and they deserve to hear those facts from their prime minister, not in allegations sprawled across a Sunday paper.

“At the heart of this issue is a worrying lack of transparency and a prime minister who has chosen to cover up a serious incident rather than coming clean with the British public.”

The admission that Ms May was informed about the results of last June’s test came 24 hours after she refused – four times – to say if she had been aware of it.