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

Defence secretary Michael Fallon is to be forced to come to the House of Commons for a grilling on the incident, after Speaker John Bercow granted an urgent question on Trident from Labour’s former defence minister Kevan Jones.

The PM’s official spokeswoman declined to confirm or deny reports that a missile malfunctioned during the test, stating only that Mrs May was told the operation was completed successfully.

“We have been clear that the submarine and the crew were successfully tested and certified,” said the spokeswoman. “That was the purpose of the operation.

“What is also clear is that the capability and effectiveness of the Trident missile is unquestionable.”

Mrs May refused to answer questions on Sunday over her knowledge of the test, in which an unarmed Trident missile reportedly veered off course off the coast of Florida in June.

But her official spokeswoman has now told reporters that the PM was briefed on the “demonstration and shakedown” operation undertaken by HMS Vengeance on its return to service following a refit.

The PM was informed that the operation was successful, allowing Vengeance and its crew to return to service.

The spokeswoman told a regular Westminster media briefing that, as a matter of long-standing policy, the Government did not publicly discuss the operational detail of exercises of this type.

The general secretary of the Campaign for Nuclear Disarmament, Kate Hudson, said: “It has become clear in the last 24 hours that the Government acted to cover up a very serious incident involving Britain’s nuclear weapons system.

“This calls into question the legitimacy of the Parliamentary vote on Trident replacement that took place in July 2016.

“MPs should have been told about the safety and reliability issues with the Trident system before they committed to spending £205 billion on a new version of the same technology.”

But Ukip defence spokesman Bill Etheridge said any faults in Trident should not be discussed in public.

“Whilst the failure of a missile test is a grave matter, is it one that should be discussed in the public arena?” he asked.

“Surely it would be better for the experts in that field to be allowed to analyse and correct the fault without hindrance.”