The Church of England has rejected claims that the Roman Catholic Church has overtaken it as the country’s dominant Christian denomination.
More Catholics than Anglicans attended Sunday church services in England last year, according to new research.
However, Church of England leaders have disputed the statistics, saying that they were misleading and did not provide a fair comparison.
The Church was nevertheless put on the defensive by the figures, which coincided with the long-predicted news that Tony Blair had converted to Catholicism on Friday.
Mr Blair was brought up in the Church of England but his wife, Cherie, is a practising Catholic.
The former prime minister was received into the faith at a service in the private chapel of Cardinal Cormac Murphy-O’Connor, the head of the Catholic Church in England and Wales.
Critics are certain to use the developments to intensify their demands for the Church of England to be stripped of its historic established status.
According to predictions by the independent Christian Research organisation, an average of 861,800 Catholics attended Sunday services in 2006, compared with 852,500 Anglican worshippers.
Peter Brierley, the former executive director of the organisation – which helped compile the data for The Sunday Telegraph – said that Catholic congregations had been swollen by the large influx of immigrants from eastern Europe in recent years.
“There’s been a substantial number of Poles coming in and 85 per cent of them are Catholic so that’s going to boost numbers,” he said.
A spokesman for the Catholic Church said that the figures for Mass attendance sounded “about right”, although he stressed that there were no precise statistics.
But a representative of the Church of England said that Christian Research had seriously underestimated its churchgoing numbers.
The Rev Lynda Barley, the head of research for the Church, said that official statistics for 2006 had not yet been compiled, but she expected them to be broadly in line with the usual Sunday attendance figures of 2005, which were 993,000.
She said that Christian Research based its figures on just one Sunday, whereas the Church conducted a detailed head count of worshippers over four Sundays in October to produce an average.
She added that, as Anglicans were not under the same obligation as Catholics to go to church every Sunday, a more accurate comparison was the average attendance at all Church of England services, both weekday and Sunday, over a month. That figure stood at 1.7 million, she said.
She said that while the Church of England encouraged adherents to go to worship weekly, many who only went once or twice a year could consider themselves full members of the Church.
Historically, Catholic Sunday attendance has been higher than that of Anglicans, but it has faced a steeper fall in recent years. This is now being offset by immigration.
The Dean of Southwark, the Very Rev Colin Slee, said: “The figures are quite misleading. They provide no reasonable comparison. The dioceses of London and Southwark have been growing for 10 years.
“In the Church of England we have 1.7 million people coming to church over a month. I don’t think that represents decline at all.”
The dean said that he wished Mr Blair “good luck” over his reception into the Catholic Church, saying that it could be extremely difficult for married partners who worshipped in different denominations.
But Mr Blair received a less warm welcome from some Catholics, including his fellow convert and politician Ann Widdecombe, the former Tory minister, who suggested that double standards may have been involved.
“At the point you are received you have to say individually and out loud, ‘I believe everything the Church teaches to be revealed truth’,” said Miss Widdecombe, who converted in 1993.
“That means if you previously had any problems with Church teaching, as Tony Blair obviously did over abortion, as he did again over Sunday trading, you would have to say you changed your mind.
“And I think people will want to know that he did go through that process, because otherwise it will seem as if the Church did make an exception for somebody just because of who he is.”