Asked about his relationship with the 86-year-old Queen on the weekend of her Diamond Jubilee celebrations, Cameron said he had found his weekly meetings with her of "huge benefit".
He paid tribute to her as an "extremely devoted public servant".
"I think that she, in pursuing her duties, has been 100% dedicated, professional," the British Prime Minister said while speaking on the BBC's Andrew Marr Show.
"It's hard to think of ever her putting a foot wrong. And you get the sense with her that she will go on doing the amazing job she's been doing for this country as long as she possibly can and you never see any sign of her devotion getting any less," he said.
"Her insight and her sharpness is extraordinary and I don't see any sign of her working less hard," Cameron said.