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British lawmakers are seeking reassurances about the nation's nuclear deterrent after a test of the system failed dramatically last month when an unarmed missile crashed into the sea near the submarine from which it was launched.
It marks the second time in eight years that the country's Trident II ballistic missiles have malfunctioned during trials.
An "anomaly occurred" during the test on board the nuclear-powered submarine HMS Vanguard, a UK Ministry of Defence spokesperson said on Wednesday in a statement.
"We are confident that the anomaly was event specific, and therefore there are no implications for the reliability of the wider Trident missile systems and stockpile," they said.
Britain's Trident nuclear deterrent system suffered an earlier failure off the coast of Florida in June 2016, a US defence official with direct knowledge of the incident previously told CNN.
The latest incident, first reported by The Sun newspaper, occurred during an exercise on January 30 near Florida.
A source told CNN that The Sun reporting was accurate and the submarine crew completed the drill perfectly using a dummy warhead. The Trident II missile and dummy warhead were propelled into the air but the first-stage boosters of the missile did not ignite and it subsequently sank into the ocean.
The fault was specific to the test kit and that the launch would have likely been successful if it had occurred out on a patrol, using a real nuclear warhead, according to the source.
The Ministry of Defence confirmed that UK Minister of Defence Grant Shapps was on board the HMS Vanguard at the time of the test anomaly. The First Sea Lord Admiral Sir Ben Key was also on board.
"As a matter of national security, we cannot provide further information on this, however, we are confident that the anomaly was event specific, and therefore there are no implications for the reliability of the wider Trident missile systems and stockpile,″ the ministry said.
"The UK's nuclear deterrent remains safe, secure and effective," it added.
Shapps said in a statementthat the test anomaly had "no implications for the reliability of the wider Trident missile systems and stockpiles".
"Nor are there any implications for our ability to fire our nuclear weapons, should the circumstances arise in which we need to do so," he said.
The Defence spokesperson said the test "reaffirmed the effectiveness of the UK's nuclear deterrent, in which we have absolute confidence".
"HMS Vanguard and her crew have been proven fully capable of operating the UK's Continuous At-Sea Deterrent, passing all tests during a recent demonstration and shakedown operation (DASO) – a routine test to confirm that the submarine can return to service following deep maintenance work," the spokesperson said.
John Healey, the opposition Labour Party's spokesman on defence issues, said reports of the test failure were "concerning."
"The defence secretary will want to reassure parliament that this test has no impact on the effectiveness of the UK's deterrent operations," he said.
The UK has four nuclear-powered ballistic missile submarines, each of which is armed with American-built Trident II D5 missiles, according to the Royal Navy. The missiles can be fired at targets up to about 6400 kilometres away.
The annual cost of the UK's Trident II D5 missile inventory, which it shares with the United States at a facility in Georgia, was about $US15.1 million ($23.1 million) as of 2015, according to a House of Commons research briefing.
Annual running costs of the UK's nuclear deterrent are estimated at six per cent of the country's defence budget, or about $US3.79 billion ($5.79 billion) for 2023/2024, according to the House of Commons Library report.
The current Vanguard-class submarines are expected to be replaced by four new Dreadnought-class submarines, as soon as the early 2030s.
The UK has set aside between $US39.1 billion and $US51.7 billion for the new, upgraded submarines, the report said.
The Virginia-class submarines Australia is buying from the US are nuclear-powered but do not carry nuclear weapons such as the Trident.
