Previous estimates have placed the number of Muslim converts in the UK at between 14,000 and 25,000, but Faith Matters's study suggests that the real figure could be as high as 100,000, with as many as 5,000 new conversions each year.
Britain has witnessed a rise in Islamophobia since September 11 and the London July 7 attacks, but figures reveal that this has not adversely affected the number of people converting to Islam.
By using data from the Scottish 2001 census – the only survey to ask respondents what their religion was at birth as well as at the time of the survey – researchers broke down what proportion of Muslim converts there were and then extrapolated the figures for Britain as a whole, The Independent reported today.
Researchers polled mosques in London to try to calculate how many conversions take place a year. The results gave a figure of 1,400 conversions in the capital in the past 12 months which, when extrapolated nationwide, would mean approximately 5,200 people adopting Islam every year.
The figures are comparable with studies in Germany and France which found that there were around 4,000 conversions a year. Fiyaz Mughal, director of Faith Matters, admitted that coming up with a reliable estimate of the number of converts to Islam was notoriously difficult.
"This report is the best intellectual 'guestimate' using census numbers, local authority data and polling from mosques," he said.
"Either way few people doubt that the number adopting Islam in the UK has risen dramatically in the past 10 years," he said. Inayat Bunglawala, founder of Muslims4UK, which promotes active Muslim engagement in British society, said the figures were "not implausible".
He said: "It would mean that around one in 600 Britons is a convert to the faith," he said. "Islam is a missionary religion and many Muslim organisations and particularly university students' Islamic societies have active outreach programmes designed to remove popular misconceptions about the faith," he said.