Analysis: Porritt whispers in PM's ear with all the force he can muster

Listen to yesterday's Sustainable Development Commission report on nuclear power and you will hear something uncommon, fascinating and slightly awe-inspiring: the sound of a big beast in the environmental jungle, getting his retaliation in first.

Jonathon Porritt has come a long way since he was one of the founders of the Ecology Party (which subsequently became the Green Party), and then leader of Friends of the Earth. Now, as chair of the SDC, and Tony Blair's official environmental adviser, he is part of the government establishment.

But only to a degree. Sir Jonathon may be an Etonian by schooling and a baronet by title but he has remained radical in his green convictions, and one of those, which he shares with most other environmentalists, is that no good whatsoever can come of nuclear power.

He clearly sees the current Energy Review as a stitch-up, a cosmetic exercise to prepare the way for a new generation of nukes, and let's be honest, many would agree with him. The common perception is Tony Blair has taken the decision already.

But unlike most green activists, Sir Jonathon can actually do something about it. His position at the head of the SDC gives him direct access to Mr Blair and potentially enormous influence, and in certain circumstances, he has to be listened to. This is one of those circumstances, and he is making the most of it. He's not waiting for the outcome of the Energy Review; he's making a determined attempt to sway the result.

Yesterday's SDC report and accompanying papers represent the most thorough, hard-hitting and detailed case against the British nuclear option which has yet been produced. This is not green soundbite, this is serious stuff. It will have to weigh in the argument. It certainly raises dramatically the political stakes for Mr Blair - and for Mr Brown when he takes over - in opting for atomic power once again.

Mr Blair has never been anti-nuclear (he likes shiny modern technology). But he has been especially persuaded of the necessity of a full new nuclear-build programme to fight climate change, by the Government's chief scientific adviser, Sir David King. Sir David has been whispering in one Blair ear; Sir Jonathon is now whispering in the other, although perhaps whispering hardly does justice to the force of yesterday's report.

The reason Sir Jonathon may ultimately not succeed is that the detail of the arguments against nuclear, displayed so powerfully yesterday, is not what is going to count. Few people would dispute that there is no solution yet to nuclear waste, or that nuclear economics are uncertain, or that a nuclear programme would partially lock the UK into a centralised energy system, or that there is a major security risk associated with nuclear energy. It's all true.

But the essence of the argument Sir David King has put to Mr Blair is that climate change is so threatening that nuclear is essential despite all that.

But you can't say the other side of it hasn't been made properly now, in the struggle between David and Jonathon for the ear of the Prime Minister.