Tony Blair's spokesman once said "We don't do God." He certainly does now.

The former British Prime Minister has gone public over his beliefs in a major speech on faith, saying religion had to be rescued from extremism in an era of growing globalisation.

Speaking in Westminster Cathedral yesterday evening against a noisy backdrop of anti-Iraq war protesters, Blair launched an impassioned defence of religion. Blair, who converted to Catholicism last year after stepping down as premier, rejected the notion that religion was divisive, irrational and harmful and argued "Faith can transform and humanise the impersonal forces of globalisation."

"For religion to be a positive force for good, it must be rescued not simply from extremism - faith as a means of exclusion - but also from irrelevance," he added.

Politicians in the United States speak openly about religious faith but Blair has admitted that if you do so in Britain "frankly people do think you are a nutter (crazy)."

When Blair was once pressed in an interview about his beliefs, his press spokesman Alastair Campbell interrupted and said 'We don't do God.'" But Blair, now working as a Middle East peace envoy and seeking international consensus on global warming, did concede religion and politics could be uncomfortable bedfellows as leaders who talk about their faith "may be considered weird."

The worst danger, he said in his speech, was that "you are somehow messianically trying to co-opt God to bestow a divine legitimacy on your politics."

After England's break with the pope in Rome during Henry VIII's reign more than 400 years ago, Anglicanism became the dominant religion. But now Britain is an increasingly multicultural and secular society.

Research published in December showed that Catholicism is now the most popular Christian denomination with more worshippers attending mass than Church of England services.