A U.S. official confirmed to CNN on Monday that the test of a British nuclear missile, conducted off the coast of Florida last June, ended in failure.
The confirmation comes after the British newspaper Sunday Times reported that the British government had covered up the failed launch, briefing Prime Minister Theresa May on the incident but keeping Parliament in the dark before ministers voted to renew the nuclear weapons system in July.
On the BBC's "Andrew Marr Show" over the weekend, May dodged questions about the test four times.
And British Defense Secretary Michael Fallon followed that up on Monday by refusing to give out "operational details" of the test while speaking to MPs, in what anti-nuclear campaigners say is another example of the post-Brexit administration's continued resistance to transparency.
Fallon would not confirm or deny to ministers that the test of an unarmed Trident II D5 ballistic missile went off course, veering toward the U.S. coast and then diverting into the ocean, which it is programmed to do when it detects an anomaly, according to CNN.
"I can assure the House that the capability and effectiveness of of the United Kingdom's independent nuclear deterrent is not in doubt," Fallon said. "The government has absolute confidence in our deterrent and in the Royal Navy."
Shadow defense secretary Nia Griffith said that for the Labour Party, "This is just not good enough."
"At the heart of this issue is a worrying lack of transparency and a prime minister who's chosen to cover up a serious incident, rather than coming clean with the British public. This House, and more importantly the British public, deserve better," Griffith said.
Another Labour MP, Mary Creagh, pointed out that CNN received confirmation before ministers, and asked why the British people were the "last to know" about the failure.
"The cover-up continues," said Kate Hudson, general secretary of the Campaign for Nuclear Disarmament (CND). "Michael Fallon has refused today to answer why Parliament wasn't told about the Trident Missile Crisis and he has rebuffed calls for greater transparency, ignoring an invitation to appear at the Defense Committee."
"It's clear the government cannot be trusted to tell MPs and public the truth about the crisis. That's why CND is calling for a Trident Inquiry," Hudson said. "This debacle also 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 (roughly $255 billion) on a new version of the same technology. "