Downing Street is being accused of a cover-up after a malfunction in Britain's Trident nuclear weapons deterrent in a test just weeks before a crucial House of Commons vote.

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

Image: The exact cause of the failed missile test remains a secret. File pic

MPs are now demanding an inquiry and are calling for a Commons statement from Defence Secretary Michael Fallon on Monday.

The cause of the failure remains secret, but a naval source told The Sunday Times that the missile - which was unarmed for the test - may have veered off in the wrong direction towards America.

"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," the source told the paper.


"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."

Image: MPs want Defence Secretary Michael Fallon to make a Commons statement on Monday

The incident happened shortly before Theresa May became Prime Minister, but she made no mention of the failed test when she persuaded Parliament to spend £40bn on new Trident submarines in her first big Commons speech in a lengthy debate on 18 July.

After five hours of debate, MPs voted in favour of Trident renewal by 472 votes to 117, a majority of 355, on a motion backed by almost the entire Conservative Party and more than half of Labour MPs.

It was opposed by all Scottish National Party MPs, the Lib Dems and Labour leader Jeremy Corbyn - a lifelong unilateralist who spoke out strongly against the plans during the debate.

Speaking to The Sunday Times, the Labour MP Kevan Jones, a former defence minister and strong supporter of Trident, has called for an inquiry into the failed missile test.

"The UK's independent nuclear deterrent is a vital cornerstone for the nation's defence," he said. "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."

Image: HMS Vengeance returned to the sea in December 2015 after an extensive refit

But a Ministry of Defence spokesperson told Sky News: "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."

According to The Sunday Times, the Trident missiles have been test-fired only five times by UK submarines this century because they each cost £17m.

The previous tests - in 2000, 2005, 2009 and 2012 - have all been widely publicised by the Ministry of Defence and Lockheed Martin, the weapon's US manufacturer, as demonstrations to the world of Trident's reliability.

The 2012 test was attended by VIPs, and a film of the launch both inside and outside the submarine was released on the internet.

But the failed Vengeance test last June was followed by a complete news silence by the British government and the missile's manufacturer.

Image: The Sunday Times says there was 'major panic' in the highest levels of government after the failed test

In December 2015, HMS Vengeance returned to sea for the first time in four years after an extensive refit including the installation of a new missile launch system.

It undertook months of tests culminating in the test-firing of a Trident missile.

The Sunday Times source said the test took place about the time of the Brexit vote on 23 June.

Three days earlier, a warning was issued to pilots to avoid "hazard areas" over the Atlantic due to "a missile launch/splash down".

It appears that HMS Vengeance's missile was intended to be fired 5,600 miles to a sea target off the west coast of Africa.

But the Sunday Times source claimed the missile suffered an in-flight malfunction after launching out of the water. The source believes this led to it veering off target.

The failure means it is 16 years since Vengeance has successfully fired a missile but it has, nonetheless, returned to active service.