The Queen has blamed the "complacency" of her subjects for the circumstances which led to the 2008 financial crisis.
Her comments came during a tour of the Bank of England's gold vaults in which she was heard to attack the failures of the regulatory system under the New Labour government.
"People got a bit lax... perhaps it is difficult to foresee," she was heard to say.
This is not the first time the Queen has questioned Britain's failure to see the financial crisis coming. In November 2008 she asked academics at the London School of Economics: "Why did nobody notice it?"
Sujit Kapadia, a member of the Bank's financial services committee, explained to the monarch that the City of London had got "complacent" because it believed it was better managed than it actually was.
The financial system had become too interconnected, he argued.
The Queen agreed, saying: "People got a bit lax, perhaps it was difficult to foresee."
The Duke of Edinburgh went further, wondering: "There's not another one coming, is there?" He then told bankers: "Don't do it again."
She added she thought the regulatory authorities "didn't have the teeth" to stop the biggest risk-takers in the City.
The Duke of Edinburgh warned executives not to let it happen again.
Mr Kapadia said after the visit: "It was an honour to be asked, and a real pleasure to be able to offer some explanation. I think she recognised that these things are very difficult and it's not a straightforward exercise."
The Queen's aloofness from the everyday conflicts of British political life is viewed by constitutional experts as being at the heart of her popularity.
But she has occasionally strayed into making political comments - as in September this year, when it emerged she had expressed frustration that radical Muslim cleric Abu Hamza could not be deported. The BBC subsequently apologised for revealing her views.
Her visit today concluded by signing a million pound note for the Bank's distinguished visitors' book, for the ninth time in her life. The first came on November 29th 1937, when she was 11 years old.
Commenting on her signature, she observed: "It hasn't improved much, you know."