Brighton College headteacher and political biographer Anthony Seldon has spent the past 18 months searching for the "real" Tony Blair.

His two-part Channel 4 documentary In Search Of Tony Blair begins tomorrow. Reporter Frankie Taggart was given a preview.

Ten years after he stepped to power as Labour leader, Tony Blair remains a national enigma.

His persona as a fresh-faced idealist and man of the people has been shattered, most significantly by the war on Iraq.

Now many are struggling to understand what remains behind the faltering smile.

Blair's biographer Anthony Seldon, a leading historian and the headteacher of Brighton College, spent 18 months scouring Britain as he built up a picture of the Premier from his early life to his place at the right hand of the President of the United States.

He has spoken to more than 500 of Blair's friends, enemies and colleagues for a major new biography, Blair, and the documentary marking the tenth anniversary of his leadership of the Labour Party.

The film, In Search Of Tony Blair, offers an insight into Blair's early life and explores his relationship with religion and how this has affected his premiership.

Dr Seldon said: "I think the tragedy of Tony Blair is when he thought he was being his most morally right that he made his most fundamental error which has undone his second term in power and undone his entire premiership. When the epitaph is written on Tony Blair's grave there'll be the word Iraq."

Dr Seldon went back to the Prime Minister's early life in Durham to reveal how during his early years as Labour leader he idolised Margaret Thatcher and even met her in secret for advice on foreign affairs.

He reveals how Blair's mother Hazel became a key influence and how he was galvanised by the suicide of his best friend to transform himself from a rebel and drifter into a serious politician and committed Christian.

During the two-hour film, Dr Seldon suggests Blair was imbued with the confidence that drove him to become Prime Minister by his mother.

He said: "Hazel's role in his life has been underestimated. She was the person who gave him this boundless self-confidence, this ability to think that he could bring the whole world with him."

The first great trauma in Blair's life came at the age of 11 when his father Leo had a stroke. Leo became determined his children should get on in life and he sent his son to the exclusive Edinburgh public school Fettes.

Schoolfriend Nick Ryden tells Dr Seldon: "One of Tony's skills was, of course, brinksmanship. He knew how far to push something and then withdraw. He became a master at that."

But while his friends recalled his rebellion with affection, Blair is remembered disparagingly by some of his masters, who marked him out as a troublemaker and almost had him expelled for protracted "bolshiness".

The documentary reveals for the first time how the suicide of Blair's best friend, Ewan MacDonald, deeply affected him and transformed him from a "hippy type" into a driven man who realised every day was precious.

The 19-year-old Blair had just started university at Oxford in May 1973 when he heard MacDonald had jumped from a bridge in the centre of Edinburgh.

Nick Ryden says: "This was someone we knew, someone we'd actually spent five years with at boarding school so we knew Ewan very well. He was actually a closer member of our family than our real families, we had been together for so long. It really hit us. It hit Tony very badly.

"I think it was a wake-up call. Despite the long hair and stuff, maybe it was a time to review life and what people were doing."

Ewan's death coincided with Blair turning to the Christian beliefs which would later shape his politics.

Dr Seldon said: "What happens at Oxford is, there's a process where he starts taking Christianity seriously. Friends notice, for example, that a Bible appears by his bedside, he goes to chapel, he's confirmed. There is a revolution going on within him."

Blair's university colleague Andrew Burn remembers: "He was a very bright and bubbly, charismatic kind of guy who immediately rose to the surface of what was a very frothy society."

Blair's political career began after university when he and his new wife Cherie Booth joined the Labour Party in Hackney. He had a lucky break when he won the safe Labour seat of Sedgefield.

Dr Seldon's documentary exposes the ruthless way in which Blair undermined his close friend Gordon Brown to become leader, destroying their close friendship.

The historian spoke to people Blair had chosen to brief against Mr Brown, saying he would not be a good leader because he was not a family man.

On the afternoon of Labour leader John Smith's death ten years ago, Blair went to see Peter Mandelson, who had assumed Blair would be loyally supporting Mr Brown.

Mandelson said: "He asked me what my attitude would be towards his desire to stand for the leadership. To be honest I was rather taken aback by his determination to stand, the sense that it was the right thing for him to do and not to allow anyone or anything to stand in his way."

On July 21, 1994, aged 41, Tony Blair became the youngest Labour leader to date.

Dr Seldon says: "If he's going to take the crown it means there are going to be bodies on the floor - principally Gordon Brown's - but he somehow reconciles this because he feels there's a higher purpose and that higher purpose is him leading the Labour Party and leading them to victory and there's no one else on Earth who can do it as well as he can."

In Search Of Tony Blair explores the relationship between Mr Blair and controversial appointee, former Press secretary Alastair Campbell.

Dr Seldon argues that Blair's religious faith and the conviction politics that flow from it are the key to understanding his leadership.

Blair sees that to achieve a good and moral outcome the ends frequently justify unpopular means.

The documentary suggests Blair's near-messianic conviction that he was doing the right thing persuaded him to take his biggest gamble, joining George Bush in the war against Saddam Hussein.

Richard Haas, a former US State Department official, says: "If Tony Blair had gone public and said, 'There's no longer a reason to go to war,' I think that may well have put George Bush in an untenable position. So there, by what he didn't do, if you will, he may have had a tremendous or fundamental impact on the course of history."

In Search Of Tony Blair is on Channel 4 tomorrow at 7pm. Dr Seldon's book Blair is published on June 21, price £20. The profits will go to charity.