Nick Clegg lavished praise on disgraced former Cabinet minister Chris Huhne as an "effective" and "outstanding" politician.
The Deputy Prime Minister pointed out that Huhne - who faces jail along with ex-wife Vicky Pryce on Monday for swapping speeding points - had penned two chapters in a new book on environmental policy.
Speaking at a fringe event at Liberal Democrat spring conference this lunchtime, Clegg said: "Whatever is going on with Chris and Vicky...
"Not only was he an outstanding local constituency MP he was also an extremely powerful thinker and indeed an very effective secretary of state," he said.
"The fact that he has contributed two chapters on very important policies is very good to see. I hope people register that."
The chapters written by Huhne in The Green Book are titled Green Growth and Going Green Has to be Fair.
Clegg insisted he had fought alongside Huhne for the green agenda, and made a thinly-veiled attack on Tories for a "mendacious" campaign against environmental policies.
"The tensions between ourselves and the Conservatives on the environment has inevitably spilled out into public because it's very real," he said.
"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.
"I have probably spent more time with Ed (Davey), and before that with Chris, making sure the coalition Government does what it said it would do and frankly what the Conservatives said they would do - putting the environment at the heart of our policy-making.
"The centre of gravity on the right of British politics at the moment is to denigrate the importance of the environment, to conduct a systematic, misleading and mendacious campaign which some seem to suggest - or seek to suggest - that somehow protecting the environment is inimical to keeping people's livelihood protected and putting money back into their progress.
"The enemies of progress, enemies of green growth, the enemies of protecting the environment are trying to distort and warp the environmental cause into one which they will claim costs people money and jobs.
"Nothing could be further from the truth. One thing I can assure you is - Ed and I will never, ever bow to that prejudice."
His comments came after a speech by Lord Ashdown, which insinuated things could be a lot worse for the party.
In a reference to Huhne - who is due to be sentenced on Monday - he joked: "You think you've got it hard now, forget it."
He recalled when he first stood Parliament in Yeovil in the 1970s, the Liberal leader at the time, Jeremy Thorpe, was facing trial at the Old Bailey.
Former energy secretary Huhne received a warm round of applause from the hall in Brighton last night when party doyenne Baroness Shirley Williams hailed his "brilliant" performance in government.
She described his downfall and that of Pryce as a "domestic tragedy".
"We can only say of them that this is a tragedy that sometimes overcomes people, not least those in public life," she told the audience.