Prime Minister Theresa May faces growing demands to give honest answers to MPs in Parliament about a failed test of the Trident nuclear deterrent.
Mrs May refused to answer questions on Sunday over her knowledge of the test, in which an unarmed Trident missile reportedly malfunctioned off the coast of Florida in June.
The Prime Minister was criticised after failing to disclose whether or not she knew about it, just weeks before MPs approved the £40 billion Trident renewal programme in July, and is being urged to come clean.
Asked if knowledge of the failed test could have influenced the MPs' decision, shadow defence secretary Nia Griffith told BBC Breakfast: "We don't know because we don't know exactly what happened, so we can't speculate on that until we have a full report, and that's what we're calling for today.
"The incident itself speaks for itself, if the reports are true, that a missile veering off course is something to be extremely concerned about.
"But we need to have the full detail of exactly what did happen and why this occurred."
Appearing on BBC One's The Andrew Marr Show on Sunday, Mrs May repeatedly refused to disclose whether she knew about the failed test before her speech to MPs, instead saying she had "absolute faith" in the Trident system.
Ms Griffith said the issue was so important that Mrs May "certainly should" have answered questions on it.
She told the BBC: "It's such a serious incident she is bound to have known and what she needs to tell us is did she know before she gave a major speech on Trident just days after she became prime minister.
"It's not the sort of thing you would forget if you had been briefed about it in the preparation for that speech."
The apparent cover-up over the failed test, involving an unarmed Trident II D5 missile launched from a British submarine, prompted widespread criticism and incredulity.
Labour peer and former senior Royal Navy officer Admiral Lord West said it was "bizarre and stupid" not to tell anyone about the test, suggesting the Government had acted like North Korea in covering up the news.
Labour leader Jeremy Corbyn called the failed test "a pretty catastrophic error", while the SNP's Nicola Sturgeon has called for "full disclosure" about who knew what and when.