Former prime minister Tony Blair's conversion to Catholicism means he is now a member of the most popular Christian denomination in Britain, according to religious research published on Sunday.

Despite England's official break with the pope in Rome during Henry VIII's reign more than 400 years ago, making Anglicanism and the Church of England dominant, Catholicism is now the most practiced faith in the land.

A survey by the group Christian Research published in the Sunday Telegraph newspaper showed that around 862,000 worshippers attended Catholic Mass each week in 2006, exceeding the 852,000 who went to Church of England services.

Attendance at Anglican services has almost halved over the past 40 years as the country has grown steadily more secular, the research showed, with only Pentecostalism showing any rise in popularity among Christian denominations.

While attendance figures for both Catholic and Anglican services are declining, Catholic numbers are slipping by a lesser degree as new migrants arrive from east Europe and parts of Africa, boosting Catholic congregations.

"When a former prime minister becomes a Catholic, that must be a sign that Catholicism really has come in from the cold in this country," Catherine Pepinster, the editor of Catholic weekly The Tablet, wrote in the Sunday Telegraph.

"I would hope that my fellow Catholics will welcome Tony Blair into the Church as they welcome other converts."

Cardinal Cormac Murphy-O'Connor, the head of the Roman Catholic Church in England and Wales, led the service. He told BBC Radio 2's Good Morning Sunday: "It was a very moving occasion.

"I suppose for him [it was] the end of a process, in the sense that he's been thinking about becoming a Catholic for a long time.

"But also, in another sense it's a beginning, because when you become a Catholic, as so many people who have become Catholics have said to me, it's like coming home.

"This was a gift for Tony, a personal journey, a gift for his family."

Cardinal Murphy-O'Connor said Mr Blair was converting from Anglicanism to Catholicism "partly because... the example of his family, his children have been brought up as Catholics.

"I think also it's not just in his travels as prime minister, but even before that, there was something he said to me, that he feels at home in the Catholic Church in a way that he didn't in any other Church, or in the Anglican commune."

Blair, now a Middle East peace envoy, is not the first high-profile Briton to convert to Catholicism.

The author Evelyn Waugh, the son of an Anglican churchman, converted in the 1930s, and novelist Graham Greene was a noted convert, although his books often explored doubts over faith.

Blair's conversion was long expected - his wife and four children are practicing Catholics - but it has not come without a degree of criticism.

While in office, he frequently championed stem-cell research, was in support of civil partnerships for gay couples and has voted in favour of abortion, all issues on which the Catholic faithful hold strong positions.

Politicians, including some who have converted themselves, didn't question the sincerity of the conversion, made in a private ceremony on Friday, but wondered what it said about the stances he had taken on issues while in office.

Mostly though, the reaction was muted.

"In the 19th century when someone 'poped' it caused great scandal," wrote the Right Reverend Richard Harries, a former bishop of Oxford, in the Observer newspaper.

"But in recent decades a fundamental shift has taken place ... If someone shifts their allegiance, well, as Jesus said, 'there are many dwelling places in my father's house'."