Theresa May knew about the test of a Trident nuclear missile system just before a vote over its renewal took place, Downing Street has confirmed.

The malfunction itself was not out of the ordinary, with a Whitehall official telling Sky News: “It was always the plan to publicise the test until it went wrong.”

The decision not to publicise the failed test was the Cameron administration’s fault, says a senior Conservative MP.

Julian Lewis, who chairs the House of Commons defence committee, commented for City News Radio minutes before Downing Street confirmed the Prime Minister had been briefed about the failed test.

Downing Street confirmed the PM knew of the missile launch /PA
Downing Street confirmed the PM knew of the missile launch /PA

“The people who should’ve been clear about it were the people who were in control of the government at the time when this test-fire took place in June,” said Lewis.

“Unfortunately, the Cameron period in office was marked by a number of occasions where party politics was played with the nuclear deterrents, beginning in 2010 when the decision was taken to put off this debate and vote until after the 2015 election. And that was done solely to suck up to the Liberal Democrats and coalition and I denounced it at the time.”

Lewis, who has authored several titles on nuclear deterrents, said delaying the vote was “an appalling decision.”

Still, while Lewis attributed the cover-up to “Cameron and his spin doctors”, the MP told BBC Radio 4’s Today programme that Theresa May’s government would have to explain what happened.

“This sort of event is not one you can play both ways. These tests are routine but infrequent in this country,” he said. “Whenever they work, which is 99% of the time, film is released of them working, so whichever person decided they wanted to draw a veil over one that didn’t work should have been sacked.

“You have always got to assume that something like this will come out.”

The unarmed Trident II D5 missile malfunctioned when launched from the British submarine HMS Vengeance off the coast of Florida. It may have veered back towards the US rather than heading in the direction of west Africa, according to details in the Sunday Times.

Weeks later, during May’s first major parliamentary vote as Prime Minister, MPs voted overwhelmingly to spend up to £40bn replacing Trident, to the dismay of the SNP and Labour party leader Jeremy Corbyn.

Defence secretary Michael Fallon has been summoned to the Commons after Speaker John Bercow granted an urgent question over the matter.

Nia Griffith, the shadow defence minister, remained adamant that the Conservative government should address the failed test immediately.

Defence Secretary Michael Fallon is expected to answer an urgent question in the Commons today/PA
Defence Secretary Michael Fallon is expected to answer an urgent question in the Commons today/PA

“Personally, I would be very surprised if they did not come [to Parliament]. I think they’ve created a very embarrassing situation for themselves and the sooner they can start putting things right, the better.”

Griffith refused to comment on whether the failed test would lead Labour to push for another vote on renewing Trident, but said transparency and accountability were the key issues at stake.

“I think it’s very very embarrassing indeed to be finding this out from a newspaper report – we don’t know the exact details of what happened, so first and foremost we now need to know that. Quite clearly, the Prime Minister would remember if she’d been told something like this, and she would know if she’d been told about it before or after she gave a very important speech in that debate on the Trident vote in July.”

The Prime Minister drew gasps at the time for saying she was prepared to authorise a nuclear strike which killed “100,000 men, women and children”.

Tune in to City News Radio today at 2pm for Griffiths’ and Lewis’ full interviews.