Struggling into his jacket as he talks, John Reid is running late for a cabinet meeting. But there is one last thing he wants to say, and he frowns in concentration as he searches for the right words to describe his relationship with the Chancellor, Gordon Brown.

'He's an immense talent of this party, he's made a huge contribution to it, I have the greatest respect for him - as I have for Charles Clarke, Alan Milburn, Tessa Jowell and other ministers,' he says.

'I believe that when one member of the Cabinet does well it raises and brings benefit to the rest of cabinet. It's not a zero-sum game, where if one does well it diminishes others.'

Not everyone, however, sees it that way. John Reid - a former young Communist turned fixer to Neil Kinnock and now valued member of Tony Blair's inner circle - is increasingly being promoted by some around Downing Street as the 'Stop Gordon' candidate in a future leadership contest - the last Blairite left standing who could see off a coup from the Chancellor. It is a potentially poisoned chalice, and he knows it.

Insisting that he is not a contender, 'and I'm certainly not a "stop anybody" candidate', Reid argues that gossip about clashes between the two camps is now hampering the party's ability to thrash out serious ideas. 'It should be possible to have a debate on the very important issues facing the country - how we balance the limitations of the market and the limitations of the state - without it being constantly portrayed as intrinsically related to personal animosities.

'Even though we may be having a mature discussion, people will portray it in this way. So what are we supposed to do? Stop thinking? Stop discussing, stop debate?'

There is not much chance of that. If there is one thing the Health Secretary likes, it is an argument - and, verbal headbutting of Today programme presenters notwithstanding, the more densely intellectual the better. He is fast carving himself a niche as the man who can push a fiercely Blairite agenda, but cloaked in the language of the old left. One colleague recalls Reid quoting the early 20th-century social historian R.H. Tawney at length in a cabinet meeting - to the bafflement of John Prescott, who misheard Tawney for 'Tony'.

If he does not exactly wear his learning lightly - his sometime use of the title 'Dr', which refers to a PhD in West African history rather than a medical qualification, has prompted some sniping - Reid has his reasons. The son of a postman from a pit village near Glasgow, the first time he saw his father cry was when Reid junior told him he'd got his doctorate: he believes powerfully, as his father did, in education as the means of empowering the working classes.

Now he is adapting that argument to push through the concept of patient choice in the teeth of resistance from doctors, arguing that only by putting power back in the hands of patients will those who have no money finally be able to play the system like the rich.

'To those who have misgivings about it, I say two things: firstly, I will protect the founding principle of the NHS of equal access to healthcare provided free at the point of need,' says Reid.

'And the second is I will never apologise for the extending to the mass of working people the privileges that have been monopolised only by the well-heeled and well-connected since time immemorial. Why on earth would we not be proud of extending that degree of information and power?'

His critics say patients would rather have a good local hospital at the end of the road than the 'choice' to traipse across the country in search of a faster operation. Reid, however, argues that the whole point of choice is precisely to galvanise all those local hospitals into doing better with the threat of losing their custom. 'If people haven't been getting that for 60 years and still aren't, should they be entitled to go elsewhere in the health service and get it?

'And if you are given that entitlement, is it more likely that the local provider will be prompted to give them a better, quicker, more personal service? I think the answer to both is yes.'

It means, he admits, a lot more uncertainty and 'flux' for hospitals, but his clear suggestion is that they have had things their own way for too long.

Reid does not much mind being on the wrong side of doctors, so long as he feels he is on the right side of patients, particularly the poorest. He horrified doctors last summer by suggesting that banning smoking in pubs could deny the working classes one of their few remaining pleasures, and is currently at odds with most of the medical profession (and, it is rumoured, even some Department of Health officials) over the government's plans to extend pub licensing.

A formerly hardened drinker who went teetotal after deciding he was a 'better person' without alcohol, Reid insists Britain's binge drinking habit is a cultural issue with its roots in the national psyche rather than pub opening times: 'I don't quite follow the argument that keeping [them] restricted will solve the problem of binge drinking, since it happens already.'

But he admits there are no guarantees that relaxing the laws will magically bring about a sensible European cafe culture either. 'Whether or not by changing the law it will ultimately change the culture and diminish binge drinking is something that will not be proved until we are able to look back with hindsight.'

As for more sensitive issues, colleagues whisper his views can be socially conservative: that will shortly be tested, with his department facing a series of complex decisions about abortion law. The chief medical officer, Professor Sir Liam Donaldson, is currently investigating claims that the government-funded British Pregnancy Advisory Service arranged for women who were over the time limit for legal abortion to get terminations in Spain; a high-profile court case is pending over a doctor who allegedly agreed to abort a baby on the grounds it had a cleft lip, a minor deformity. Pro-life MPs are preparing to use both as springboards for a parliamentary attempt to restrict the right to abortion.

Reid voted for terminations to be available only up to 18 weeks of pregnancy, rather than the current 24, when the issue was last before parliament. He refuses to say now what his personal views on abortion are, but insists he will respond 'without fear nor favour' on it as Health Secretary: 'I try to stand against both those who would wish to extend beyond what parliament wanted, but at the same time be very wary in making sure that I oppose those who wish to use these attempts to restrict what parliament has decided.' He will not, he says, be drawn on 'hypotheticals' about how he might vote.

As for that other great hypothetical question hanging in the air - that of the vacancy that will arise when Tony Blair quits during the next parliament - Reid says the speculation about his prospects 'hurts me', pointing out that he and Brown have known each other since they were students. Privately, he has told colleagues that the only reason he enjoys Downing Street's favour is precisely because he is one of the few who don't covet Blair's job.

Yet with other hopefuls falling by the wayside - Alan Milburn remains undecided over whether to make a permanent comeback once the election is over, while rising stars from David Miliband to the Work and Pensions Secretary, Alan Johnson, are still too untried yet to be in the running for Downing Street - the Westminster rumour mill is casting around for a credible leading man. Reid may well find himself fitting the bill.