It must be Gordon, Gordon, Gordon

David Miliband is the new foreign secretary so we thought this was good moment to look back to Septe

One issue has defined Tony Blair's legacy, perhaps destroyed it: foreign policy, or rather Iraq, the Middle East crisis and the Prime Minister's uncritical support for George W Bush. Over the summer, as Israeli forces swept north across the border into Lebanon, even the most loyal ministers could not take it any more. One of them was David Miliband, a former policy chief at Downing Street and everyone's next-leader-but-one.

Miliband, who had just been promoted to Environment Secretary, was reported as telling a cabinet meeting at the end of July: "Where is this all going to end?"

Until this past week, Miliband has refused to elaborate, for fear of undermining further a leader who has treated him well. But this has not been one of those ordinary weeks in politics. Many MPs saw Blair's refusal to call for a ceasefire in Lebanon in the first weeks of the conflict as the last straw. So how did Miliband feel about it?

"I don't think anyone was relaxed about the situation," he says. He does not deny making the remarks to cabinet. "I felt very worried because, put it this way, I don't think that Israel is safer and stronger now than it was two months ago. I don't think the prospects of a secure and just two-state settlement in the Middle East are closer than they were two months ago."

Miliband's approach to international affairs is based on a different understanding of Britain's role from that of his older cabinet colleagues. His group of politicians - the thirty- and fortysomethings - sees no need to prove his party's credentials towards America or anywhere else. Ronald Reagan's refusal to meet Neil Kinnock in 1987, in protest at Labour's anti-nuclear position, is, to Miliband, ancient history. To others it is not, and this is where the difference lies.

As Labour MPs collect signatures demanding Blair's resignation, the generational issue looms large. We put to Miliband Charles Clarke's suggestion in last week's New Statesman that Labour runs the risk of returning to the splits of the early 1980s and to a long period in opposition. He is dismissive: "I think it is ridiculous to talk about civil war in the Labour Party. We are talking about, with perfect confidence, our chances of a fourth term. I don't see a civil war and I think that is inflammatory rancour."

Members of the cabinet are now throwing themselves into the debate increasingly publicly. Miliband was happy to speak openly of the Prime Minister being gone in 12 months. His interventions on the issue are marked by a growing personal belief that, at the age of 41, he has ample time to fulfil his own ambitions. Having ruled himself out of the leadership this time around, he also makes clear he will not stand for deputy leader when John Prescott goes. "I'm neither a runner nor a rider for any of the contests."

Train crash

Miliband turns to the generation game. "I think there are many people who are more or less in my position: we weren't scarred by the battles of the 1980s in the same way that the people who went through them were, and we look at the current debate through a different lens. We look at the debate which says, 'Either we have a smooth transition or you have a train crash.' Obviously you want a smooth transition. But we want something more. These are people who are ministers, who are party MPs, party supporters; these are people of no party, who are in the voluntary sector or business or the public sector, and they want an energetic, progressive project. So what I believe is that we need more than a smooth transition to Gordon Brown - we need an energising, refreshing transition to Gordon Brown."

The message to cabinet colleagues such as John Reid and Alan Johnson (men in their late fifties) is clear: stand if you wish for the leadership, but you have no chance. Your time is past. His message to Blair's outriders is: stop looking for an alternative and get behind one man. Mili band explains: "The great mass of the labour movement is in a very pragmatic, central position. It is proud of what the government has done over the last nine years. It is excited about the prospect of a Brown leadership. You can keep those two thoughts at the same time and I think that most people do."

He is keen to distance himself from Blairite "ultras" such as Stephen Byers and Alan Milburn, the former ministers whose calls for a "thorough debate" to embed the Blairite legacy for the next decade are intended to tie Brown's hands. But nor does Miliband believe in closing off all discussion about the future direction of policy as some Brownites have suggested.

So, amid the frenzy about the Prime Minister's future, shouldn't Brown be speaking out more, or at least setting out his agenda for the future? "It would be a bit cheeky of me to tell him how to do his job. What is incumbent on people like me is for us to stay upbeat, and he can decide when and how he wants to do it. I think he will be a very good leader."

Brown may have been around for 20 years in top-flight politics and he may have been hanging around for a decade for the top job, but Miliband insists he has much more to offer. He is adamant that Brown represents the start of something new, not the tail end of the Blair years. The term he uses repeatedly is "transition".

"This isn't about endings - it's about beginnings. It's about launch pads; it's about foundations for further change." Again, it seems to come down to age: "People of my generation believe several things absolutely to their core. New Labour is not an aberration, the Blair era is not an aberration. The Tories want it to be an aberration because they like the idea that the Labour Party puts itself into impossible positions and gets itself slaughtered. Some on the left also hope it's an aberration. But it's not. There's no going back to the fairy-land economics of the 1980s. There's no going back on the idea that with investment comes reform in public services, that you need accountability. One was the lesson of the 1980s; the other was the lesson of the 1990s."

Opening the shutters

But these twin lessons, he argues, are not enough. "You need more than the rear-view mirror. You need more than the lessons about not repeating our mistakes of the 1980s, learning the lessons of the 1990s. You need a different sort of politics if you are to address 21st-century problems. You do need to open the shutters intellectually, organisationally. You can't have taboos about this. We mustn't have a divisive, rancorous [argument]."

And, in order to avoid any doubt, he names the next leader again. "We can have an energising, refreshing transition and that's why what I would say: the transition to Gordon - just to underline - the transition to Gordon Brown, the smooth transition to Gordon Brown, the energising, refreshing transition to Gordon Brown - not to anyone else - is a transition that is about ideas and values more than about dates."

Miliband goes out of his way to depict Brown as part of the young guns' vision. And yet the Chancellor's last Budget was denounced across the eco movement as hideously ungreen. One organisation described his penalties on drivers of Chelsea tractors as amounting to little more than a cappuccino a week. Miliband is careful to defend Brown's approach towards environmental taxation, but again talks in terms of differences between the generations. "A lot of my colleagues now have grown up being environmentally conscious. If you went to university in the 1980s you had to be." The implication here is that the many grey-haired members of the cabinet have failed to keep up with the public mood.

He concedes that in the past he, too, did not pay enough attention to green issues. He recalls that, as schools minister, he was responsible for setting guidelines for new buildings. "We did write in sustainability, but did I write it in in a dramatic enough way? I could have done more."

His first four months in the new job have provided salutary lessons. His conclusions on global warming are stark. "The science is more alarming and the problems more imminent and short-term than I realised. There's no question about it." He points to research on the nine danger areas around the globe. "From the Greenland ice sheets to the Siberian ice sheets, to the Gulf Stream, you name it, it's close to the tipping point. The insurance industry will tell you, events like Hurricane Katrina will tell you - the problems are not far off, they are short-term."

As for the green concerns of that other young 'un, the Conservative leader, Miliband uses a new tack to dismiss his credentials. Much of the work on combating climate change, he says, is being done by the EU. "You cannot be an environmentalist, as David Cameron pretends to be, and be neuralgic about Europe. I want the European angle to be properly understood. The centrality of European action is critical."

Public confidence

The environmental agenda, Miliband suggests, could revive public confidence in the EU. He has high hopes for its carbon trading scheme, under which Britain has agreed to an eight-million-tonne reduction in emissions. He says the UK's target of a 60 per cent drop on 1990 carbon-emissions levels by 2050 is ambitious. With the government failing to meet its own targets and with emissions rising, however, he warns against relying too much on cleaner technology over the next 20 years to help meet the dead- line. "It is the cumulative emissions between now and 2050 that count," he says, "not simply whether you hit the target."

The environmental contract is most boldly expressed in proposals for "personal carbon allowances", which would allow low waste producers to trade surplus carbon credits. Miliband believes the scheme would be egalitarian because the poor are the lowest producers of waste. Green issues, he says, belong to the left.

"A central part of progressive policy will be understanding the need to live and work within environmental limits. Does it speak to social- democratic concerns about social justice? Yes. Does it speak to social-democratic concerns about rights and responsibilities? Yes."

One of Clarke's criticisms in the NS was the way in which controversial policy issues had been broached, by both Blair and Brown, over the years. The former home secretary was scathing about Blair's attempt to set nuclear energy policy with a one-line remark at a dinner with the Confederation of British Industry and about a similar move by Brown to pre-empt discussion on the Trident nuclear deterrent with a throwaway sentence in a speech at the Guildhall.

Miliband had said he was "open-minded" about nuclear power. He has now made up his mind, and it is not good news for the anti-nuclear lobby. "In all conscience, if I'm going to save the environment, with climate change the top priority, how can I say that, on an unsubsidised basis, nuclear can't play its part in this drive to meet the climate-change challenge?" He insists that each sector should be economically self-sustaining, that taxpayers' money should not be spent on inducements to nuclear firms, and that funding for renewable energy should be "locked in".

He is similarly forthright about the replacement of Trident. "I fought [the election], like every Labour MP, on the manifesto. You can't pick and choose which bits of the manifesto you don't like and which bits you like."

An agenda is being mapped by Miliband and his generation. It builds on the Blair years and the emphasis on economic efficiency and public service reform. But, in its approach to the environment, international affairs and other issues, it demands greater courage. And to their mind, for the next few years at least, all of this would come under the banner of one man - Gordon Brown.