The move by former director of strategy Richard Reeves will heap pressure on Mr Clegg ahead of his party's annual conference in Brighton this weekend.

The Deputy Prime Minister issued a public apology for his U-turn on university tuition fees.

In a sign the party wants to quell increasing tensions ahead of its conference, Mr Clegg used a party political broadcast to say: "There's no easy way to say this: We made a pledge, we didn't stick to it – and for that I am sorry."

Mr Reeves, who left No 10 earlier this year to move to the US, said the Brighton event would be dominated by the question of whether of not to depose the LibDem leader.

He backed Mr Clegg but called on him to stand up more to what he called the Tories' "creeping paternalism".

He said the LibDems had to be firmer on civil liberties and take a more liberal stand on social issues, including proposals for a minimum price for alcohol – a policy also being pursued by the Scottish Government.

He also called on the LibDems to decriminalise the possession of cannabis and ecstasy.

The party should also oppose new rules on cigarette sales and a crackdown designed to curb pornography use on the internet, he said.

Mr Reeves also waded into the row over Mr Clegg's suggestion that those who do not support proposals to introduce gay marriage are "bigots".

"Here's the thing," he wrote in the piece for the New Statesman "they are bigots".

The LibDems faced the brunt of public anger over the tuition fees rise, after they scrapped a pledge to oppose rises.

Within months of the Coalition being formed it was announced the charge students in England have to pay would be tripled to £9000 a year.