George Osborne needs to give up being the Tory strategy chief and concentrate on running the ailing economy, ex-chancellor Lord Lawson has said.
The Conservative grandee also urged David Cameron to start modelling his premiership on Margaret Thatcher and not on Tony Blair.
The peer did not back calls for Mr Osborne to be moved out of Number 11 in a reshuffle tipped for the autumn, despite conceding the last budget was "not his biggest success".
But he said that Mr Osborne needed to focus exclusively on the tough job of addressing the deficit following criticism that his dual role led to him taking his eye off the ball.
There was nothing to stop the Prime Minister consulting with his close ally on specific issues, as he had "on the whole a pretty good political antenna", he told BBC Radio 4's Westminster Hour.
But he added: "I do think it might be sensible to give up the formal role and focus exclusively on his job as Chancellor of the Exchequer which is a tremendously important job."
Dismissing suggestions Mr Osborne should be moved to a different role, he said: "I think his last budget was not his biggest success but I think he should continue in that job. But I do think...that it would be sensible for him to set aside his second job."
In a pointed criticism of Mr Cameron, he said the party leader had "a lot to learn" from Baroness Thatcher's methods - and was out of step with Tory MPs in favouring the recent Labour model.
"There are basically two models of long-term premiership in recent memory: Margaret Thatcher and Tony Blair," he suggested. "David Cameron has modelled himself very much on the Blair style. I think the Conservative backbenchers prefer the Thatcher style.
"I do think he has a lot to learn from her. And I think Blair is a bad role model except in that particular time in history of changing the Labour Party which had to be done. He was brilliant at that but I don't think that applies to the Conservative Party at all. I don't think there is any read across."