Nick Clegg surprised delegates at the Lib Dem conference by going out of his way to heap praise on Chris Huhne, just days before the disgraced former Cabinet minister is expected to be jailed.

The Deputy Prime Minister told Lib Dem supporters at the party's Brighton conference that "whatever happens in court" next week, Huhne was still an "outstanding" politician and "extremely powerful thinker".

Clegg used the launch of a book on the environment to praise the achievements of Huhne, who will be sentenced on Monday after pleading guilty to perverting the course of justice for asking his wife, Vicky Pryce, to accept three penalty points for speeding.

Commenting on the fact that Huhne had written two chapters of a new book shaping future Lib Dem policy on the environment, Clegg paid glowing tribute to the disgraced former Climate Change Secretary, who quit the Cabinet vowing to fight the charges before changing his plea to guilty as his trial was about to begin.

"The fact that he has contributed two chapters on very important policies is very good to see. I hope people register that," said Clegg.

The chapters written by Huhne in The Green Book are entitled Green Growth and Going Green Has to be Fair.

Clegg said tension between Lib Dems and the Conservatives on the environment had "inevitably spilled out into public because it's very real".

He went on: "I am unabashed in saying that we the Lib Dems have a crucial role to keep this government anchored in the centre ground, not to make it lurch one way or the other, not allow it to be captured by vested interests or a particular set of prejudices."

He said David Cameron's pledge to make the coalition "the greenest government ever" had been thrown off course in recent months.

Speaking to activists at an informal Q&A session later in the day, Clegg vowed to stop apologising to voters for past mistakes such as breaking a promise to oppose increases in student tuition fees.

"It's important not to be brow-beaten," he said. "As a campaigner, I know people do not hear your achievements until you have gone on and on and on about them."

On the economy, Clegg said he was "restless for growth", but conceded there was no magic solution that could produce it.

"I don't want to fool anyone by suggesting it is easy," he said. "Britain has to live within its means."

He said it was essential to get banks lending to businesses, but added that the Lib Dems have to be "candid" that economic recovery would entail a "slow, painstaking journey".

Responding to a call from the defence secretary Philip Hammond for more welfare cuts, Clegg said the Lib Dems were not opposed to welfare reform.

"The welfare budget accounts for a third of government spending," he said. "You cannot cut spending without touching it."

But he insisted that the Lib Dems wanted to protect the poorest, saying this set the party apart from the Tories.

He confirmed that the Lib Dems would cut benefits for wealthy pensioners, after Vince Cable mooted the idea in an earlier interview.