Labour MP Chris Bryant has branded BBC Director-General Lord Hall a "coward" and a top director at the broadcaster "daft".
He was taking part in a lively debate at the Edinburgh International Television Festival and accused Tony Hall of not standing up to Culture Secretary John Whittingdale.
Asked if the over-75s should have their licence fee paid, Mr Bryant said: "That is a government political decision, it is not for the BBC to decide who gets a free television licence."You shouldn't be turning the BBC into a subset of the Department for Work and Pensions. That is just morally offensive.
"And nobody suggested it in the General Election, they had no mandate to take it forward, and I think that Tony Hall frankly was a coward in not going to the public and saying 'You John Whittingdale publicly said before the General Election that you would hate any process that was just a stitch-up over money'.
"I think it's unpatriotic frankly for a Conservative party that is meant to believe in Britain to diminish the greatest British brand that we have."
Mr Bryant also called a BBC director "daft" for having welcomed remarks made by Mr Whittingdale about the future of the corporation.
During an interview at the festival, Mr Whittingdale rubbished the idea that the broadcaster is to be dismantled, saying that he has "never suggested dismantling the BBC".
Mr Whittingdale also said that suggestions that there was an ideological Tory drive to destroy the corporation were "just extraordinary".
Director of strategy and digital at the BBC, James Purnell - a former Labour MP and Culture Secretary - said the corporation welcomed what Mr Whittingdale said.
"I think he's changed the mood around the debate, very much so," Mr Purnell said.
But Mr Bryant, who is shadow culture secretary, said: "John has been appointed specifically to be the nice guy who wanders around conferences and says 'look it's not going to be so bad, it's all going to be fine'. And James Purnell's bought it. Daft. Ludicrous."
Mr Bryant said that after the General Election he predicted the first thing the Government would do would be to make the BBC fund the licence fee for over-75s.
He said everyone was claiming Mr Whittingdale would "never" do that, but the BBC has since taken on that cost.
"I think people should be very, very, very wary," Mr Bryant said. Mr Purnell also said this week that the BBC welcomes debate about its future but said it is absolutely appropriate that if it is felt there is a danger of a "diminishing" of the BBC, that they address it.
The Culture Secretary had sparked concern among some supporters of the corporation after saying that a review of the BBC's royal charter would look at whether the broadcaster should continue to be "all things to all people" or have a more "precisely targeted" mission.