Tory MP Peter Bone called it the “non-story of the year” and said voters would be refreshed by Mr Cameron’s honesty.
But a senior backbencher said: “It was a gaffe. It won’t do him any harm now, but it confirms my expectation that he will announce his departure soon after the EU referendum in 2017.”
Several MPs pointed out that Mr Cameron once said Tony Blair’s decision to rule out a full third term was “an absolute killer” for his authority while still prime minister.
Alastair Campbell, who was Mr Blair’s director of communications, said it was a “potential disaster” for the Tories.
“He has created a massive distraction,” he told Newsnight.
“I think he has opened up something that he will find very difficult now to close.”