"Oh Clare, you are a one," Tony Blair once affectionately told his Secretary of State for International Development. He may have been thinking the same again, though with less affection, on Thursday night, as Clare Short broke cabinet ranks to say what everyone else thinks - that the Millennium Dome was an expensive flop which should swiftly be put out of its misery.

Clare Short is a big beast of Labour party politics. At least as "emotionally literate" as Mo Mowlam, Downing Street knows she can never safely be assumed to be "on message".

Distrustful of spin - never more sure than when following her instinct for plain dealing - it would barely have occurred to her to maintain the pretence that the Greenwich disaster dome had been a useful exercise in urban regeneration. What's the point in spinning when nobody believes it?

The press had a field day. With Gordon Brown's credibility under serious challenge over what he knew about that £1 million Ecclestone donation, the fuel crisis rumbling on, the Tories stretching their lead in the polls, Clare Short's candour guaranteed more damaging headlines for Mr Blair on the eve of what promises to be a tricky party conference.

Interestingly, Downing Street's control freaks didn't have the time or inclination to take her on. And by yesterday she had been publicly vindicated, as Mr Blair issued his own semi-mea culpa - (an acknowledgement that the dome had not lived up to expectations).

Ms Short has no intention of wounding the Prime Minister. On the contrary, during an interview for The Irish Times, she confessed to feeling "rather protective" toward him.

Whatever the irritation caused by her comments about the dome, here is a minister who insists she won't be briefing against colleagues, seems happy to share credits with them, is unmistakably "proud" to be in Blair's government, and well able to make a convincing case for its achievements.

The job of International Development Secretary might have been made for her, her passion burning bright after three years in the post: "It's noble, by definition . . . What more noble thing in politics but to try and improve the lives of the poorest of the world?"

And does she think she's made a difference? She explains that Labour set out to get the whole international development system - the individual countries, the UN agencies, World Bank, the IMF, the African Development Bank, Americans, Asians and so on - "to be much more focused on poverty reduction, not just in rhetoric but in measurable impact." And in the common commitment to the targets and increased collaboration between the Bank, OECD et al in gathering the statistics needed to track progress, Ms Short sees the fruits of Britain's increasing influence.

"The other big thing," she adds: "Britain was a leading player on the debt-relief front. Gordon [Brown] was personally very committed to it. We helped shape a new way of working for the bank and the fund, that means countries have to do a poverty-reduction strategy which includes the debt money, all their own revenues, whatever's coming from aid, their economic policy, where their public spending is, to leverage the debt relief . . .

"These are not small things. I don't want to be boastful at all. It's just being really serious, knowing what you want, then taking the same story into all these international organisations so you can get coherence."

Does getting that coherence also mean taking on established agencies and received wisdom? "The thing with development is the rhetoric's always fine. People go to the UN from all kinds of government, all parts of the world, and speak the rhetoric of caring about the poor. And then lots of the practice is much less good," she replies.

There are always political and commercial considerations, countries "want their flag over their project" when the question is: "What does this government need to reform in itself to get every kid into school? That isn't about flags, that's building the capacity to run a sustainable primary education system."

The minister believes the $50 billion in the international development system could be more effectively spent. And the public agrees. Polling by her department found aid associated in the public mind with waste, corruption and failure.

Spend effectively and people will connect. But value-for-money aid involves hard choices, between, say, the claims of an immediate war zone and education in Africa. Ms Short is clear people must never go hungry: "But that's not development, and peoples' lives don't improve. Just offering people to keep them alive while their life actually gets worse is a miserable business."

Hard choices in the wider world of government, too. Is Ms Short comfortable that Labour's "ethical" description of its foreign policy is to be dropped from the next manifesto?

She's not for playing what she considers a journalistic "game", says Robin Cook has been unfairly taunted with the word and that he and Tony Blair have developed "a more principled" approach on arms sales, human rights and much else to which many in the international community would testify.

Ms Short "absolutely" supports the government's "prepare and decide" approach to the euro and has "no conclusion" as to how she will argue in cabinet come the moment of decision. Unlike Mr Blair, however, she does not imply the politics of the issue are already settled.

But just as another "cabinet split" headline suggests itself, the minister explains: "You see, the way the world is changing has constitutional implications. The world is globalising, a lot of economic power nation-states used to exercise they can't separately exercise any more, but they can sort of pull that sovereignty to get international rules for trade, on investment, on the environment. And this isn't a matter of choice. I mean . . . the Tory Party's railing against history."

No split there, then. Nor on much else: "We are a very boring government . . . We're probably the first Labour government ever that hasn't had a left-right split, and we genuinely haven't."

Hardly boring. Another spate of books has laid bare the deep personal loathings at the heart of this government. Ms Short accepts this is damaging but suggests this is down to "the courtiers" rather than "the real players".

One real player recently counted herself out of the game. And there are persistent suggestions that Mo Mowlam was driven out by a "lads culture" inside Number 10 which can't cope with strong, independent-minded women.

After affirmation of love for Mo, and disappointment at her decision to go, Ms Short makes clear with feeling that she despises briefings against colleagues: "We've all experienced it, and it's hateful, and it obviously hurt Mo."

She continues: "Of course you get jealousy in politics and Mo was fantastically popular - both because of the person she is, her courage in dealing with her illness, and because people were so happy about Northern Ireland moving forward to peace. All these things come together and of course you'll get jealousy."

However, Ms Short acquits Mr Blair of failing to find a role for Dr Mowlam: "As I understand it, she was offered Health." And she says the Prime Minister made the right decision in moving her from the Stormont post last year. "Mo did have to move from Northern Ireland, not because of any fault in her, but because the unionists, for whatever reason, had less confidence in her - and because the peace process is bigger than any of us, any individual."

She goes on: "So any responsible prime minister would have organised that, and Mo would obviously regret it. She deserved deep respect and a serious job because she's great and she'd done a fine job. Now I wasn't there. But the offer of Health is a serious job, it's one of the top jobs in the government, and she didn't want that. And then, you know . . . Foreign Secretary? Well, sorry, job's occupied. It then became very unfortunate and she felt disappointed, and now she's choosing to move on in her life."

Does Ms Short hope to move on, higher up the ladder? Could she be tempted by other things? "Yes, but not all. It would have to be very good to be better than this." The thing, she says, is not to get too calculating "so you're always thinking about the next job rather than the one you've got."

And what about the top job? They say no politician reaches her rank without harbouring hope of one day making it to Number 10?

Clare Short thinks that equally true of backbenchers who've never sat on the front bench. "When I was younger I would have thought that might be possible. I think I could do the job competently and well. But I'm not the kind of person that people would choose . . . and therefore I won't."