By Chris Hastings, Patrick Hennessy and Sean Rayment

The Asian tsunami disaster should make all Christians question the existence of God, Dr Rowan Williams, the Archbishop of Canterbury, writes in The Telegraph today.

In a deeply personal and candid article, he says "it would be wrong" if faith were not "upset" by the catastrophe which has already claimed more than 150,000 lives.

Prayer, he admits, provides no "magical solutions" and most of the stock Christian answers to human suffering do not "go very far in helping us, one week on, with the intolerable grief and devastation in front of us".

Dr Williams, who, as head of the Church of England, represents 70 million Anglicans around the world, writes: "Every single random, accidental death is something that should upset a faith bound up in comfort and ready answers. Faced with the paralysing magnitude of a disaster like this, we naturally feel more deeply outraged - and also more deeply helpless."

He adds: "The question, 'How can you believe in a God who permits suffering on this scale?' is therefore very much around at the moment, and it would be surprising if it weren't - indeed it would be wrong if it weren't."

Dr Williams concludes that, faced with such a terrible challenge to their faith, Christians must focus on "passionate engagement with the lives that are left".

His comments came as Tony Blair finally broke his silence on the tragedy, branding it a "global catastrophe" that would take the world "years" to deal with. The Prime Minister, who has faced criticism for not cutting short a family holiday in the Egyptian resort of Sharm El Sheikh, also insisted that the United Nations should lead the international aid effort. He praised the "extraordinary generosity" of the British people, whose donations topped ‚ £60 million last night. The Government has thus far pledged ‚ £50 million.

Interviewed by Channel 4 News, Mr Blair said: "At first it seemed a terrible disaster. But I think as the days have gone on people have recognised it as a global catastrophe.

"It is not simply the absolute horror of what has happened and how many people's lives have been touched in different ways, it is also the fact that the consequences are not just short-term and immediate but long-term and will require a great deal of work by the international community for months, if not years, to come.

"We've got millions of people displaced, we've got the potential of disease coming from this and we've got whole areas of that region that will have to be rebuilt."

He shrugged off claims that he should have come home to take charge of Britain's aid effort, adding that he had been in touch "practically hourly" with Downing Street.

Mr Blair said that one of his key tasks during Britain's year-long presidency of the G8 group of leading industrial nations, which started yesterday, was to liaise with other leaders. His faith in the UN seemed undimmed despite the international rows in the months prior to the war in Iraq and he dismissed as a "misunderstanding" claims that President George W. Bush had tried to snub the organisation by setting up a four-country task force with Australia, India and Japan.

"When I spoke to President Bush a short time ago he made it very clear that he wanted the UN to be in the lead and that he sees the work that the US is doing as very much supportive of that," he said.

Mr Blair's intervention was made as it was disclosed that Gordon Brown, the Chancellor, would lead Britain's international anti-poverty drive by going on a three-nation trip to east and southern Africa later this month.

Meanwhile, a 10-man British military reconnaissance team arrived in Sri Lanka to assess how British Armed Forces could best assist the stricken country which, with Thailand, Indonesia and southern India, has borne the brunt of the disaster.

The team will report back to the Permanent Joint Headquarters in Northwood, Middlesex, in the next 72 hours. The main focus of Britain's effort is likely to be directed towards Sri Lanka and the Maldives.

Two Royal Navy ships, the frigate Chatham, currently on patrol in the Gulf, and the Royal Fleet Auxiliary vessel Diligence, already in the Indian Ocean, are heading for Sri Lanka. A C-17 Globe Master transport aircraft, which can carry 100,000lbs of cargo, has also been allocated to supply aid.

The Pope in his New Year message yesterday led prayers for victims at St Peter's Basilica in Rome, and a prayer vigil for victims, survivors and families was being held at Central Hall, Westminster, last night.