Blair's personal chaplain from Down Under

Tony Blair's Christian socialist mentor - and best mate - has returned to London. Ian Hargreaves tracked him down for this exclusive interview in today's New Statesman

Unlikely setting. Unlikely man. The place is London N7, a quarter- mile to the west of Holloway prison, the same distance north from Pentonville. Walk 10 minutes and you're at Tony Blair's house in Islington. We're in a small flat which sits above the St Francis Church of England Centre, a bland 60s-ish brick structure which provides a meeting place for Alcoholics Anonymous, a disabled kids' group and an Ethiopian church of Coptic Christians.

The man is Peter Thomson, 60, Australian, Anglican vicar. To the extent that he's famous, it is for having inspired the young Tony Blair at Oxford towards an idea of Christian socialism which continues to drive him. But those who know Thomson can tell you that he's famous for much else: he was booted out of one curacy in Melbourne as a suspected Communist and out of a second, in Cambridge, for setting up a scrap-metal business to create jobs in his parish. He has been headmaster of one of Australia's top private schools, Timbertop, and worked in the family estate agency. He's a farmer and has read the television news on Australia's Channel 7. Now, suddenly, he's here, as Vicar of St Luke's Holloway, that is if the visa comes through OK.

So what is he doing in Holloway? "I was just waiting for something like this to come up," he says.

"When Tony became leader, things started to happen. I was getting calls from London from people asking me about our relationship and it just became very exciting. I wanted to be part of it. It sparked me up. So I talked to Tony and said that if I came to England I would want to be what I am, not to work directly in the political arena."

A few weeks ago, Blair called to say that he heard St Luke's was looking for a vicar and would Peter like to be interviewed. He combined the trip with a visit to his publisher, about a planned book with the working title Community, and got the job. Thomson's journey is worth plotting, because it reveals a lot not just about where Tony Blair found some of his most formative ideas, but because Thomson, like Blair himself, is still travelling.

Although Blair takes care not to wear religion on his sleeve, there is no doubt that Christian socialism continues to inform and define his political philosophy.

Thomson's own journey began unremarkably enough, as an impressionable I7-year-old who thought there must be a nobler thing to do than help run his father's estate agency. He went to theological college, a rather conservative one, as it happens, but through a friend encountered politics.

It was the first step towards an engagement with liberation theology - that potent blend of Marx and the gospels which tore through Latin America and elsewhere in the 1970s, preaching a militant bias to the poor. "I had never been politically challenged before and it just blew my mind - here was a basic rationale for faith that was not about personal salvation or being perfect. I could see there was a job to do."

Thomson also discovered the work of John Macmurray, a Scottish theologian who, in Thomson's view, grounded Christian thinking in action and human relationships. For Thomson, the argument is summarised in his favourite Macmurray quote: "All meaningful knowledge is for the sake of action, all meaningful action is for the sake of friendship."

It is not difficult to see why Blair, a curious observer rather than a member of the Oxford God Squad, was attracted to Thomson's blend of religion, politics, sport and riotous hilarity. "I remember the first time I met him in that Afghan coat," says Thomson, of Blair. "He wasn't particularly religious, but he was just alive. Tony had never heard theology spoken of in this way, but I had no idea just how deeply it had got to him."

After two years at St John's, Oxford, Thomson returned to Australia and, eventually, to Timbertop. The connection with the Blairs became that of good family friends. The two families spent last Christmas together, at Thomson's 200-acre farm near Timbertop.

So it is that Thomson finds himself in London, in the most testing year of Blair's life.

"I want no role other than friendship," he says. It's not entirely clear what that will mean.

Partly, Thomson sees himself as the older friend the Blair family needs as it heads towards Downing Street. It's not difficult to imagine him straying across the border to N1 to offer Tony a piece of his mind about the latest shadow cabinet battle. In a sense, he will be personal chaplain to the Blairs: that's if a chaplain can also be best mate, which in Thomson's case is not in any doubt.

But will the two men agree about ideas, as they once so resonantly did at Oxford? In Thomson's view New Labour has a coherent and vibrant philosophical underpinning. "It all starts with the word community. The idea of community represents the breakthrough of a philosophical position,'' he says. ''It means the individual has no meaning except through relationships, so that it's in community that the maturing process goes on. You can pursue the individualist line only so long as you've got other people to exploit. The Third World is now close to the point where you can't push it any more, whether on environmental issues or whatever."

At the base of human relationships, Thomson says, is the family - again a familiar Blair preoccupation. But here, there is something different. ''The family is not an issue of kin and blood. That's part of it, but I'm talking about families which exist because their members will it to be so, where people are bound together by a sense of belonging and love."

Three hours after I arrive, Thomson is still going at it hammer and tongs: politics, ethics, family genetics, history, and, when the tape recorder is off, gossip of a passionate sort. Tony Blair might have ditched the Afghan coat, but he hasn't got rid of the bloke who keeps you up half the night bending your ear.