The most influential man in British sport is a millionaire opera-lover who, friends say, does not even like sport.

Mr Patrick Carter was initially appointed by the British government to analyse the finances of the 2002 Commonwealth Games. His brief was then extended to assess the viability of Pickett's Lock as the London venue for the 2005 World Athletics Championships and the way forward for the national football stadium project. He effectively became the British government's sports troubleshooter. And he has become more influential with each new project he has taken on.

His analysis of the Commonwealth Games finances prompted the government to inject £105 million sterling (€168 million) into the event. He moved on to Pickett's Lock, where he advised the government to find an alternative venue for the 2005 World Championships. Recently, the government tried to move it to Sheffield - with disastrous results.

His role in whether the national stadium will be built - and if so, where - is set to be as critical.

As elusive as he is influential, Mr Carter is the author of a confidential report on the national stadium in Britain. In it, he outlines the available options, including that believed to be favoured by the Football Association (FA) - a state-of- the-art stadium at Wembley, capable of seating 90,000 and adorned with an enormous arch. Other proposed sites in Birmingham and Coventry were also examined in the document.

Three proposals were selected as potentially viable: a slimmed-down version of the FA's original Wembley design minus extraneous hotel and conference facilities; a "cheap and cheerful" proposal that is likely to require new planning permission but would be built on the site of the existing Wembley; and a stadium in Birmingham.

His role on the national stadium has, since he delivered his report to culture secretary Tessa Jowell last month, again been extended. He was initially asked to consider the best way forward for the project but has since become Britain's unofficial stadium guru, mediating between FA chief executive Mr Adam Crozier, Sport England, the Lottery funding body and representatives of the various bids.

All this for a man who is not even being paid for his efforts. But Mr Carter, a school friend of Foreign Secretary Jack Straw, and best man at his two weddings, is not thought to be short of money.

He is a former director of MAI, now known as United Business Media, and in 1985 founded Westminster Health Care, which went on to become the largest operator of care homes in the country. In 1999 he received more than £8 million from the sale of his stake in the business. He was also formerly a non-executive director of the prison service.

Mr Carter's prudence on Pickett's Lock and the Commonwealth Games, and his perceived neutrality, have made his recommendations acceptable, even if the government has been lambasted for following them.

Mr Gerald Kaufman MP, chairman of the House of Commons select committee on culture, media and sport, has previously been critical of the government's sports policy. But on Mr Carter he says: "I think he's done a good job and I agree with his recommendations."

Sports minister Richard Caborn said last week that Mr Carter's national stadium report, which remains unpublished, "simply underlined the obvious". Mr Caborn said the FA was given more than £100 million by way of a lottery grant from Sport England to buy the Wembley site in 1999 and this, the government feels, should be sufficient.

"My view is that Carter will recommend not going ahead with Wembley," says one senior FA source who is at the centre of talks about the future of the national stadium project. "I can't help but think that the government decided a long time ago that it did not want this (the national stadium) to happen. If it refuses to put any more money into this, the FA will say 'we're off'."

This may be brinkmanship, as neither the government nor the FA wants to be saddled with the burden of providing extra funds to an already-blighted scheme.

Given Mr Carter's prudent track record, abandoning the notion of a national stadium is a realistic possibility. After the success of Sven-Goran Eriksson's England team playing their matches at club grounds, a growing lobby at the FA - thought to include Mr David Dein, vice-chairman of the FA and Arsenal - is in favour of keeping the national side on the road.

With this in mind, together with the government's reluctance to commit extra funds and the FA's threat to walk away if no new funds are forthcoming, the dream of a new, purpose-built national stadium is unlikely to turn into reality.