The shaven-headed archbishop kneels motionless in silent prayer in front of his two-man tent. Forty pilgrims, crowded into St John’s Chapel inside York Minster, join him in his vigil: reciting prayers, sitting in meditation, lighting candles, hoping for the best.

The purple entry flap of John Sentamu’s canvas home during his seven-day “fast for the Middle East” matches the episcopal purple of his cassock. From towering ancient walls, the sun breaks through the stained glass to fleck this peculiar religious tableau with patches of light. Curious Japanese tourists peek through the grilled wooden chapel side at the praying prelate, like visitors in a zoo wondering if the lion is about to move.

Every hour, on the hour, he does move, rising from his seat to lead a seven-minute service that is piped through the cathedral on the PA system. “Darkness cannot overcome darkness,” he says. “War is a no-return journey. It is better to light a candle than to curse the darkness”.

That said, some people are still in the dark about it all. “He can’t change anything,” explains one sceptic, looking at the crowd of believers with the piercing eye of doubt. “What we need is George Bush in the tent here, he’s the one who needs to hear from above.”

“I’m worried he’s going to get ill with not eating,” says Anna, 18, who has been praying with him and looks like she could do with a hearty meal herself. “But I think it will make a difference.”

“It depends if you believe or not,” says Stan, 31. “I personally think the church has had it, but my kids are impressed.”

At the end of each short service, the pilgrims rise from their prayer and come forward to shake the archbishop’s hand: some want to congratulate him, some want to be healed or blessed. Some don’t know what they want except to be able to do something, anything, in a world in which complex international conflicts refuse to yield up simple answers and politicians lack the public courage to express their private convictions.

Nobody can quite explain what this eccentric ecclesiastical spectacle might achieve, but under the beautiful gothic awning of a medieval minster, the balance of opinion is that prayer might be worth a try. It is a peculiar postmodern setting, synthesising ancient pilgrimage with modern art-installation. While some are clearly disciples approaching a holy man praying for peace, others could be eyeballing David Blaine, fasting for attention by the Thames. No sooner has a man, about to undergo chemotherapy, asked the bishop to lay healing hands on him, than a Japanese woman tries to choreograph a digital triptych: elderly, grinning parents, the bishop at his canvas shrine.

“It’s an amazing act,” says Jong Il Kim from South Korea. “I look at him and I am shocked but impressed. It makes me think this is an important action for reconciliation in our world.”

Every now and then an archbishop hears the voice of God. For Sentamu, born in a village outside Kampala in Uganda 57 years ago and the first black archbishop in the Church of England, it happened watching a television news report. In a Lebanese village an eight-year-old girl had lost an eye and did not yet know that both her parents and brother were dead. Not so far away, in a deserted neighbourhood of northern Israel, an 85-year-old woman sat alone in her flat, the only person left to hear the rockets of Hezbollah screaming through the night.

Sentamu, who became the 97th Archbishop of York only last October, was preparing to set off with his wife Margaret and their two grown-up children on a holiday to Austria. As the crisis in Lebanon spiralled out of control, for some days he had been listening for a divine word but, disappointingly, given the precedent for divine articulation in the region, God seemed to have lost his tongue. Powerless to know how to respond to an escalating disaster, frustrated at the impotency of political leaders, agnostic in the face of e-mails asking what people of faith might do.

“I was gutted at that news report,” explains the archbishop, who does not speak received Anglican. “Gutted at the plight of the young and the elderly, at those who are helpless in this conflict. And then I realised this was what I had been trying to hear. I was hearing the voice of God in that little girl, in that old woman.”

His decision to scrap the holiday, move into a tent inside the cathedral and undertake a fast came when he read from the Bible about the disciples of Jesus failing to heal a young boy. “They ask Jesus why they couldn’t do it,” he explains. “Jesus replies that it was ‘only by prayer and fasting’. And that was my word. I thought, this is the same. It’s got to be prayer and fasting . . . ”