MUSLIM converts have an image problem. A handful, like Richard Dart, a Dorset native jailed last month, have been implicated in terrorism. Samantha Lewthwaite, who was married to Germaine Lindsay, one of the 7/7 bombers and himself a convert, is wanted by Kenyan police in connection with an alleged bomb plot.

Even without the taint of extremism, women are sometimes pitied for joining a religion accused of oppressing them. Despite these concerns, converts, for the most part peaceable, propel Islam’s transition from an immigrant religion to a home-grown one.

Calculating convert numbers is tricky. The census in England and Wales only asks about people’s current religion. Mosques do not record conversions centrally, and some new believers keep their conversions quiet. But using census data on race and religion, and questionnaires issued to mosques, Kevin Brice, a researcher at the University of Wales Trinity Saint David, reckons around 5,200 Britons turn to Islam every year, bringing the total number of converts to about 100,000.

Proselytising has little do with it. A handful of Muslim groups hand out tracts in the street. But most are more concerned with issuing press releases condemning extremism than wooing converts, says Leon Moosavi, an expert on Islamic conversions at Liverpool University.

Those who embrace Islam tend to do so after years of contact with Muslims. Reasons vary. Some, mostly women (who make up around two-thirds of new believers), want to marry a Muslim. Others are fed up with the bawdiness of British society. Many speak of seeking a sense of community. Batool al-Toma, an Irish-Catholic convert who runs the New Muslim Project in Leeds, was attracted, she says, by the spirituality of Islam and the warmth of relationships she saw among Muslims.

For men, prisons have proven a fertile ground for conversions. Just over 11,000 prisoners are Muslims, about 13% of the total. Last year an inquiry by the home affairs select committee named prisons as a breeding ground for radicals. But a study by the prisons inspectorate in 2010 produced a more positive conclusion. Converts, a third of those interviewed, said the discipline and structure of Islam helped them to cope with prison life. Others cited the support they received from their Muslim “brothers”. Some were initially attracted by the prospect of a cushier spell in jail—more time outside their cells, for example, and better food at Ramadan, but then completed their conversion.

Upon release though, some prisoners are shunned by their fellow Muslims, says Tracey Davanna, who studies Muslim prisoners at Birmingham University. Ex-cons are not the only ones who find integration tough. Many mosques are ethnic clubs, says Mr Moosavi, and can be unwelcoming to converts. Few mosques offer substantial support to new converts. Organisations such as the New Muslim Project have sprung up to fill the gap. It provides certificates of conversion that new believers can leave with their wills in case appalled relatives refuse an Islamic burial. Two mosques in Britain are now run by converts. The Ihsan mosque in Norwich encountered antagonism from some Muslims, says Uthman Ibrahim-Morrison, who has been a member of the community since the mid-1990s. Some questioned whether new believers should be in charge of a mosque, he says. But it has flourished. At Friday prayers they struggle to squeeze everyone in.

Despite successes like this, fears persist that this home-grown Islam will produce more Mr Darts and Ms Lewthwaites, intent on havoc rather than faith. New-foundzeal may leave converts vulnerable to radical strains of Islam. Isolation from their old life and lack of integration with moderate believers can only make that risk worse.