LONDON — British Prime Minister David Cameron said Queen Elizabeth II keeps him on his toes with some sharp questions during their weekly meetings. Cameron said he found the Wednesday evening audiences “therapeutic” as the 86-year-old sovereign puts the country’s problems in perspective. Cameron’s comments came in a documentary called “Our Queen,” to be broadcast Sunday on ITV television. The documentary follows the story of the 2012 diamond jubilee year, the queen’s 60th on the throne. As a constitutional monarch, Queen Elizabeth is politically neutral but has a right and duty to express her view on government matters. The sovereign has the right to be consulted, to encourage and to warn. The meetings with her prime ministers are strictly confidential — no notes are taken and nobody else is present. Cameron is the 12th British prime minister to serve under Queen Elizabeth. The first was Winston Churchill. “There’s a very therapeutic side to it, because as you explain the particular problem that the government has, or a particular challenge the country’s facing, sometimes you find it is all becoming clearer as you explain it to this one incredibly experienced person,” Cameron said. The Conservative leader said he was “very conscious” that he was the 12th British prime minister that the queen has dealt with. “She’s been listening to this stuff for 60 years … and you get some pretty good questions which you need to think of some good answers to,” he said.