Sir Michael Fallon is to be quizzed by MPs today over claims that Downing Street covered up a Trident missile test failure just weeks before a crucial Commons vote.

The Defence Secretary will be forced to make a Commons statement or answer an urgent question after Theresa May refused four times in a TV interview to say whether she knew about the malfunction.

The Sunday Times has revealed that a Trident II D5 missile veered off course after being launched from the British submarine HMS Vengeance off the coast of Florida in June last year.

Defence Secretary Michael Fallon speaks to media in front of HMS Audacious at BAE Systems, Burrow-in-Furness, where he will attend a steel-cutting ceremony to formally commence production of the UK’s next generation of nuclear… It happened only weeks before Mrs May became Prime Minister – but she made no mention of the failed test when she persuaded Parliament to spend £40bn on new Trident submarines on 18 July.

After five-hours of debate, MPs voted in favour of renewing Trident 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.

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

Asked in an interview on the Andrew Marr Show if she knew about the test failure when she spoke in the debate, which was one of her first big tests as PM, Mrs May repeatedly refused to answer.

Theresa May answers Andrew Marr’s question on the Trident failed test ‘cover up’ “I have absolute faith in our Trident missiles,” she said. “It was about whether or not we should renew Trident, whether we should look to the future and have a replacement Trident.

I think we should defend our country, I think we should play our role in NATO with an independent nuclear deterrent. Jeremy Corbyn thinks differently.

Pressed three more times on whether or not she knew about the missile failure, Mrs May again dodged the question, saying: “There are tests that take place all the time regularly for our nuclear deterrents.

What we were talking about was a very serious issue.

Responding to the PM’s refusal to answer questions, Mr Corbyn told Sophy Ridge on Sunday on Sky News: “We understand the Prime Minister chose not to inform Parliament, and instead it came out through the media.

It’s a pretty catastrophic error when a missile goes in the wrong direction and while it wasn’t armed, goodness knows what the consequences of that could have been.

Nia Griffith, Labour’s shadow defence secretary, said: This report of a Trident missile veering off course during a test is clearly a very serious matter indeed, and we need to know exactly what happened.

Furthermore, it is completely unacceptable that today the Prime Minister chose to side-step questions on the test, and would not even tell us when she knew about the incident.

I am demanding the Prime Minister come to Parliament to give a full explanation to MPs.

The Scottish National Party’s Westminster leader, Angus Robertson MP, said: “The Prime Minister must come to parliament this week and outline exactly what she knew and when about this reported malfunction and alleged UK government cover up.

It would be utterly unacceptable, and deeply serious, if it turns out that this information was deliberately kept from MPs at the time of the renewal vote for the Trident weapons of mass destruction programme.

Parliament and the public have a right to know if these reports are true, and there must be full disclosure about what happened, who knew, when they knew, and why the House of Commons wasn’t informed. The Prime Minister cannot continue to dodge the question.

Admiral Lord West says it was stupid advice to cover up the failed test Tory MP Dr Julian Lewis, who chairs the Defence Select Committee of MPs, told Sky News the blame for the cover-up rested with former prime minister David Cameron not Mrs May.

If she has said anything about it she would have had to point a finger at the previous government, said Dr Lewis. I am afraid the Cameron administration has a bad record of playing politics with the nuclear deterrent.

And the Labour peer and former First Sea Lord Admiral Lord West said: I think it is bizarre and stupid that they didn’t say that there’d been a firing and that there had been a missile malfunction and that it was a minor fault.