IN London, city of the damned, they still don't quite know what to make of Gordon Brown. What manner of a man is he? It is as if he has landed from a planet previously unknown to astronomers. To some he is "psychologically flawed" while to others he is a dour control freak who wouldn't trust a lollipop lady to take him across a road. His glass - even when he is watching his beloved football - seems always to be half-empty. He has the faraway look of someone not entirely engaged with those around him. Yet he is unignorable, the sort of person who can put a damper on the most joyous of occasions, who could ruin the carnival atmosphere in Rio simply by being in the vicinity. When he smiles he does so sinisterly, like Don Corleone. In short, he is to everyone but his most intimate circle an enigma.

The word most often used to describe him is Presbyterian. But what is a Presbyterian? What do they do? In what do they believe? Well, they work ceaselessly, sing in a manner which suggests they are doing so through gritted teeth, talk at you not to you and never do anything to draw attention to themselves. The model is John Knox, defamed as the man who rendered Scotland a dark, melancholy and miserable place in which to spend one's Earthly existence. "Knox," reflected Robert Louis Stevenson, "had a grim reliance in himself, or rather his mission; if he were not sure that he was a great man, he was at least sure that he was one set apart to do great things." For Knox, one might well read Brown.

"Presbyterians don't do frou-frou," explained one quasi-Presbyterian metropolitan commentator recently. "Indeed, we aren't naturally inclined to a whole raft of things: high style, expensive food, showy holidays. The fact that Brown served Sainsbury's champagne at his own wedding says it all. We are hopeless on magic and miracles."

Brown is not only a Presbyterian but a son of the manse, the first since Bonar Law in 1923 to occupy 10 Downing Street. In England the phrase may be meaningless, but north of the Border it is freighted with significance. To be a son of the manse means you are a minister's son, and thus exposed daily to life's defining events. Living in a manse in Kirkcaldy in the grey 1950s, Brown once recalled, he learned a lot about life and death and the meaning of poverty, injustice and unemployment.

How his upbringing will influence his premiership remains to be seen. However, in a speech announcing his candidacy, Brown gave myriad clues. Featured prominently was the notion of community. The Britain he envisaged was one in which if you work hard, you'll be better off. If you save, you'll be rewarded. "If you play by the rules, we'll stand by you," he promised.

"For me, my parents were - and their inspiration still is - my moral compass. The compass which has guided me through each stage of my life. They taught me the importance of integrity and decency, treating people fairly - and duty to others."

To anyone brought up in the Church of Scotland such sentiments will sound eerily familiar. Moreover, to a son - or daughter - of the manse they will be doubly so. One such is Wendy Alexander who, if the runes are right, is on course to succeed Jack McConnell as leader of the Labour Party in Scotland. Thus there is the tantalising possibility - depending on the fortunes of the SNP - of a son of the manse in power at Westminster and a daughter of the manse installed as first minister at Holyrood. For the Kirk, which seems permanently to be in a state of crisis and corrosive navel-gazing, this would represent a remarkable coup. Not that it would ever see it as such. That is not the Kirk's way. The suppression of ego is taken as read. Like its followers, the Kirk is not given to triumphalism or attention-seeking demonstrations of celebration. Hubris is not in its lexicon. Earthly success is irrelevant. Its mind is on higher things. It's all about how you acquit yourself come Judgement Day when the Lord runs his eye over your moral balance sheet.

The first thing to remember about Presbyterianism, Alexander tells me, late one afternoon at Labour's Glasgow headquarters, is that it is founded on the tradition that we are all equal in the eyes of God. "As an individual, it's not about what you achieve but who you are that is important in life." Secondly, she adds, there is the centrality of the parish which the minister serves. "In that sense, the children of the manse grew up in an environment where building community is what's going on around your family life all the time."

Though she and Gordon Brown shared the same faith and traditions, Alexander emphasises that her upbringing and her experience of life in a minister's household was quite different. Born in 1963, she spent her first seven years "living above the shop" at Community House, the Glasgow base of the Iona Community. Winters were spent in the city while in summer the family decamped to Iona, the cradle of Scottish Christianity. Every week in Glasgow, in the room immediately below the family flat, there were meetings of War On Want, Gamblers Anonymous and Alcoholics Anonymous. "I would come home from school in primary one and lay the table for the lunch for homeless people, which was held every single Wednesday."

As she walked through the Gorbals she witnessed its demolition: an entire community bulldozed out of existence. An inchoate sense of injustice slowly developed. Then, come summer, it was off to Iona where every morning "we walked with my father across the Street of the Dead to the 10 past eight service". Every day she would recite: "I wake my soul and with the sun the daily stage of duty run."

"That stays with you," she says.

The formative influence on her father's life - and hers by extension and osmosis - was George MacLeod, the charismatic founder of the Iona Community. In his award-winning biography of MacLeod, Ron Ferguson recalls how at youth camp on the island he would sit at the table, take a fork and spin it and ask the person to whom it pointed whether he or she was a Christian by conviction or convention. Or he would confront some hapless person with the question: "Are you a Christian or a Presbyterian?"

Once, MacLeod said grace then asked the student sitting next to him if he had kept his eyes closed duringit.Douglas Alexander,Wendy's father,replied that he hadn't,he'dbeentoo busy praying. MacLeod asked him what he was planning to do with his life. Alexander père said he wasn't sure, but he was considering the possibility of the ministry. "Come down to the Abbey tonight, I'm giving a series of lectures," said MacLeod. "By the end of it you'll want to be a minister."

"I'd never heard anything like it," remembered Douglas Alexander later. "And I did want to be a minister by the end of it."

In the conservative, cautious, reserved Church of Scotland, MacLeod was seen by many as a maverick and radical. Left-tilting at best, he was regarded by some as a communist. According to Ron Ferguson, MacLeod admired "the communists' passion for social justice and wished it would be matched by Christians".

Through her father, Wendy Alexander inherited MacLeod's reforming zeal. The same might be said of another son of the manse, Sir David Steel, the Scottish parliament's former presiding officer. Like Douglas Alexander, Sir David's father - also called David - was an acolyte of MacLeod's, inspired by his desire to use his ministry to improve the living conditions of people in Govan in the 1930s.

Sir David, who was born in Kirkcaldy in 1938, says he realised quite early on that being a son of the manse marked him out as different. For a start, he says, the tradition was that the minister's family sat in the front pew in church. "I suppose you were very conscious of the fact that it was your father in the pulpit." Sundays were sabbatarian and he was not allowed out to ride his bike or play in the street. It was the Lord's Day and he had to attend two church services and Sunday school. He was also expected to observe a more strict standard of behaviour than most other children. Once, he recalls, he saw a man selling flowers in the street, so he and his brother picked bunches of bluebells from the manse garden and did likewise. One customer was the local provost who reported him. "My parents were absolutely horrified. We got into terrible trouble."

As was the norm, the Steels moved around parishes, invariably inhabiting manses which were draughty and under-heated and lacking in creature comforts. On a recent visit to the manse in Linlithgow where he had stayed, he was amazed to find it now has central heating. "We didn't have central heating," he says sorrowfully.

Manses were generally large, imposing houses which were difficult and costly to keep up. Their size was partly in respect of the minister's status in the community. Manses, says Sir David, had to accommodate many functions. It was where parish meetings took place and the minister had his study and library. Everyone was welcome, from down-and-outs to lord lieutenants. Manses, though, were not owned by the ministers. Nor were they always well-maintained. As Harry Reid pointed out in Outside Verdict: An Old Kirk In A New Scotland, it is still relatively common to hear stories of ministers having difficulty in getting even minor repairs dealt with.

"The peculiar nature of the manse," writes Reid, "which is often as much an office and a meeting place as a home, makes it less of a retreat than the family home is for most professional people. It is difficult, if not impossible, for most ministers to ring-fence their domestic life."

TheKirkwasall-encompassing.Whenthe American theologian Reinhold Niebuhr came to Scotland in 1947 he said that Americans were more "church-minded" than any other nation, "with the possible exception of Scotland". Sons and daughters of the manse would agree. Apart from Sundays, which were given over to worship and Bible study, the rest of the week involved one church-related activity after another. If, like Gordon Brown and David Steel, you were in the Boys' Brigade, your entire free time could be spent in its embrace, either honing marching skills, learning how to tie a perfect tourniquet, playing the drums or attending Bible class. Keeping the uniform clean and gleaming entailed tedious hours spent Brassoing buckles and blanco-ing haversacks. Then there was the Youth Fellowship, the Women's Guild, the choir and countless other organisations and activities.

"In middle-class suburb, rural community, or huge housing scheme," recalled Johnston McKay, BBC Scotland's former editor of religious broadcasting, "the social role of the church was clear and unquestioned." It was the social hub of the community, the place where people naturally congregated. For children, the Sunday school was key, providing in the 1950s and 1960s a safe environment for "young, immature" girls in which to develop.

Moreover, reflected McKay: "There was an importantsocialsidetomanySundayschools.The annual Sunday school trip of a town or city congregation was an important social event right up until the 1970s, when car ownership became widespread and foreign travel offered more glamour than a day in the countryside. Its heyday was in the 1950s and 1960s, when fleets of hired buses took sometimes hundreds of children and parents often to a field in the country, or to a seaside venue, where an advance party of adults, often making use of a lorry made available by a church member or parent, had set up benches brought from the church hall, boiled large urns of hot water to make gallons of tea, marked out an area where the races' were to take place, and had prepared a vast number of paper bags containing perhaps two sandwiches, a cake and a biscuit. Sometimes meat pies were offered from a nearby bakery and delivered hot to the field."

Such scenes would have been very familiar to Gordon Brown and Wendy Alexander. Underpinning it all, however, was the Presbyterian doctrine. "There is something about the Scottish tradition," says Alexander, "which is about how you give witness in life. Not evangelism, but witness in life against the backdrop of faith. And so that did mean we used to have meatless meals every Wednesday because it was a way of contributing to Christian Aid and there were long discussions about that. Was that a much better way to give than to sponsor an individual child who would then have an experience so different from the rest of their community? I had more cheese soufflés in five years than I ever want to have again."

TheKirkinwhichAlexanderwasnurtured was also heavily politicised. George MacLeod, for example, stood as the Labour candidate in a rectorial election for Glasgow University and the Iona Community and was regarded by some in the Kirk as a Jesuitical conspiracy pushing the Kirk simultaneously towards Catholicism and Communism. Consequently, writes Ron Ferguson: "Iona Community members found the doors of many parishes in Scotland closed to them: they were seen as dangerous men. Divinity students contemplating joining the Community were warned about their career prospects."

MacLeod made no excuses for his involvement in politics, citing Knox and the Covenanters as precedents. "If churchmen are not politically involved, you soon get the spectacle of RCs and Communists dominating our trade unions - as now they do," he wrote in reply to one critic.

"As to Labour choice, it is not a bad thing to introduce the Faith into Labour policies, which, left to secularists, could indeed veer into Communism ... What matters even more is the continuance of democracy as a living cause in our midst and not the Labour, or any other party, in permanent ascendancy. But to achieve this Christians must be involved."

MacLeod's manifesto was received warmly by the likes of Alexander. MacLeod, she says was the "hero" of her family. As a two-year-old in 1965, she recalls, she was taken to the Scottish premiere of The War Game, which imagined a Soviet nuclear attack on Britain. In her circle, membership of the Campaign for Nuclear Disarmament was common. However, she was not originally destined to go into politics. "I was always going to study medicine," she says, her intention being to become a missionary in Africa. "I had to face up to the fact that I would not be a good missionary. It was a much more difficult decision than any other I've taken. Leaving office she resigned as a government minister in May 2002 was no big deal in comparison to facing up to yourself, and coming to terms with the fact that this is not what I want to do or will do well."

Alexander's torment at not pursuing her original vocation lingers still. She is, she says, very different in that regard to her brother Douglas, the Secretary ofStateforInternationalDevelopmentat Westminster, who is five years her junior and who thereforedidnotshareherexperienceofthe hothouse atmosphere of the Iona Community. What they do have in common, however, which all sons and daughters of the manse share, is a sense of duty and purpose and an urgent need to serve. For Wendy Alexander, this manifests itself in her hunger to build communities and her ambition to wipe out poverty. For Gordon Brown, it is realised in his desire to create a society in which everyone has equal opportunities. For Sir David Steel, it made him passionate about the ending of apartheid. It is, says Sir David, instinctive. And whenever he meets the Alexanders or Gordon Brown, he says, despite theirpoliticaldifferences:"Thereisasortof instinctive unspoken bond."