The role of religion in the public square is the key challenge facing the world, according to former British prime minister Tony Blair.

Writing in UK Catholic magazine, The Tablet, he asked: “Is it a force for good or a force for ill? A force for healing or for conflict? A force of reaction or a force for progress?”

“How these questions are answered will, in many ways, determine the spirit and the events of the 21st century.” Mr Blair said.

Religion, he said “has a right to be heard but not dictated” in the public square.

However, he said “politics today is inclined to treat religion as something that ought to be a private individual matter. . . a voice of conscience, not of counsel and profound insight.”

The Victorian era “saw an extraordinarily robust vitality in this respect with the building up of . . . religious organisations as safety nets for the poor”. The post second World War boom suggested such organisations had become “superfluous”, yet faith-motivated groups emerged to serve the marginalised.

Mr Blair said he believed that the world was moving into a period when interfaith action will come into its own. In that complex context Pope Benedict’s encyclical Caritas in Veritate was “a powerful call . . . that resonates both ecumenically and with the deepest moral sentiments of the different world religions”.

He continued: “We are, understandably, preoccupied with the threat posed to us by violent religious extremism.”

However, there was a broader issue at stake, Mr Blair said. Religious extremism could also be expressed “in the idea that a person’s identity is to be found not merely in their religious faith, but in their faith as a means of excluding the other person who does not share it”.

Mr Blair added that he was not saying “that it is extreme to believe your religious faith is the only true faith. Most people of faith do that. It doesn’t stop them respecting those of a different faith or indeed of no faith.”

Faith was problematic when it became “a way of denigrating those who do not share it as somehow lesser human beings. Faith is then a means of exclusion. God in this connection becomes not universal but partisan, faith not a means of reaching out in friendship but a means of creating or defining enemies.”

When it came to religious identities, “intrareligious dialogue is no less important than interreligious dialogue – often a necessary counterpart – and equally difficult, because of real differences”.

Rapid globalisation and revolution in communications made this more difficult. On one hand, “the boundaries of religious faiths are becoming more permeable, and their content more eclectic”, but on the other hand, “they are hardening into a stridently defensive or threateningly aggressive rejection of difference, with hatred and fear as the inevitable consequence”.