London (CNN) -- The BBC has apologized to Britain's Queen Elizabeth II after a reporter revealed the monarch was "pretty upset" that British officials had failed to arrest radical Muslim cleric Abu Hamza al-Masri.
Usually private conversations with members of Britain's royal family remain private. But in an extraordinary breach of this convention on BBC Radio 4, security correspondent Frank Gardner said the queen told him she had asked a government official why Hamza remained at large during his days as the imam of a mosque in London.
The revelation that the queen had personally lobbied a government official over Hamza, convicted in Britain for soliciting murder and inciting hatred in 2006, came as Gardner was discussing Hamza's probable extradition to the U.S. on terror charges.
Speaking to Today program host James Naughtie, Gardner said: "Actually, I can tell you that the queen was pretty upset that he was, this man was, there was no way to arrest him. She couldn't understand why -- surely there must have been some law he must have broken. Well in the end, sure enough there was. He was eventually convicted and sentenced for 7 years for soliciting murder and inciting racial hatred."
Naughtie, clearly taken aback by Gardner's revelation of a private conversation he'd had with the queen, called the disclosure a "corker" and said, "That's a fascinating piece of information, Frank." Gardner replied: "Yes, I thought I'd drop that in -- she told me."
Gardner said: "She spoke to the home secretary at the time and said, 'surely this man must have broken some laws, why is he still at large?'"
The queen rarely expresses her opinions -- let alone political views -- in public. Her role is to stay above politics, so Gardner's disclosure is a rare insight into how she privately engaged with Britain's government on a specific subject.
CNN's Royal Correspondent Max Foster says the convention for anyone meeting the queen at a palace event is that the conversation is private. He said: "If you accept the invitation, you accept that anything said is off the record."
In a statement on its website, the BBC wrote: "This morning on the Today programme our correspondent Frank Gardner revealed details of a private conversation which took place some years ago with the Queen."
"The conversation should have remained private and the BBC and Frank deeply regret this breach of confidence. It was wholly inappropriate. Frank is extremely sorry for the embarrassment caused and has apologised to the Palace."
When reached for a comment, a Buckingham Palace spokesman told CNN: "We never comment on private conversations."