Nothing unites warring factions so much as a common enemy and, as 650 bishops left their encampment in Canterbury to march on the capital yesterday, they at last had a single purpose. They set aside their civil war over sexuality and went out to vanquish world poverty.

But the only heat in this battle was caused by the blazing midday sun as the column of purple moved slowly and silently past the Houses of Parliament towards Lambeth Palace.

The standards they held aloft all proclaimed the same polite message: “Halve poverty by 2015 — Keep the promise.”

The Archbishop of Canterbury, Dr Rowan Williams, was in the vanguard — not with a shield but a big blue plastic banner. It called for the millennium development goals to be fulfilled within the promised eight years; at the current rate of progress this deadline will not be met.

Dr Williams told The Times that the purpose of the march was to “persuade other governments, through our government, to keep up the pressure on poverty”.

The Archbishop's entourage were in the centre to keep up morale and ensure that the message got through.

The Bishop of London, the Right Rev Richard Chartres, said: “We have got people here in the front line in the civil war in Sudan, people who are crossing the line in North Korea, so we come here with people who see so clearly the impact of poverty.

“It's a demonstration — not an angry one, not a violent one — to say to politicians we expect the promises made to be kept.”

The Bishop of Durham, the Right Rev Tom Wright, stood shoulder to shoulder with him. “We're here to say that the Church, which has been at the forefront of alleviating poverty, is not going to let this issue go,” he said.

Cardinal Cormac Murphy-O'Connor, head of the Catholic Church in England and Wales, who had joined the troupe for the day, said: “What this does is show that there are things that are extremely important that unite us all.”

The march was a joint operation with Micah Challenge, a Christian charity working to achieve the millennium development goals.

Andy Clasper, its executive director in the UK, said: “The Church is in the front line in the war against poverty, reaching parts of countries that governments can't reach.”

For Bishop Peter Munde, from southern Sudan, poverty and war are a daily reality in his diocese and he said that the march could help to unite the fractured and fragile Church. “The Anglican Communion will unite as people see us walking together.”

One of the key players in the civil war engulfing the Anglican Church, the Most Rev Katharine Jefferts Schori, presiding bishop of the Episcopal Church in America, said that the development goals would be achieved only if “wealthier nations did their part”.

After reviving from the heat on rations of Fairtrade chocolate and fruit juice, the troops massed in Lambeth Palace courtyard to hear from their leader and his guest of honour, Gordon Brown.

The Archbishop presented the Prime Minister, who was sporting an ecclesiastically coloured purple tie, with a letter setting out his plan of campaign for putting an end to poverty.

He told his men (and women) that “the divisions between people are larger than they have ever been” and “the gulfs seem to grow deeper all the time”.

Unless the gaps of development between human beings were bridged there could be no future for anyone, he said, adding that it was central to the Christian faith that “when one part of the body suffers, it all suffers”.

Then the Prime Minister congratulated those gathered and said the march had been “one of the greatest public demonstrations of faith that this great city has ever seen”.

He praised them for the work they had done upholding the cause of the poor and, knowing his audience and as a true son of the manse, quoted three times from the Bible. “In the words of Amos, justice will flow like water and righteousness like a mighty stream,” he said

The march should not just be from Lambeth, he said, but to New York, where the UN will have an emergency session in September to discuss world poverty.

In ancient Rome, Cicero gave speeches and people said “great speech”, Mr Brown said, but in Ancient Athens (and it felt as hot) when Demosthenes spoke people turned to each other and said: “Let's march.”

And then everyone went for lunch.