Up to eight people, suspected of having links with extremist groups such as Al Qaeda, are working in Britain's police service, a media report claimed on Saturday.
Citing an intelligence service file, The Daily Mail said the serving officers are believed to have attended training camps in Pakistan or Afghanistan.
They figure on a secret list drawn up by Britain's domestic intelligence service MI5 in the aftermath of 7/7 terror attacks in London, it said.
However, many of them have not been sacked because the police do not have the legal power to dismiss them, it said.
Instead, the suspected staff are unofficially barred from working in sensitive posts and are closely monitored, the report adds, identifying 'political correctness' as the reason for not sacking them.
Meanwhile, Pakistan is the source for the majority of the clerics in Britain, with only eight percent being born in the UK, a study has said.
The study carried out by Chester University of 300 mosques in Britain found that 50 percent of the head clerics were from Pakistan, 20 percent from Bangladesh and 15 percent from India.
Around 66 percent spoke Urdu as a first language with 52 percent delivering sermons in Urdu.
Only six percent of those preaching in the UK spoke English as a first language, The Daily Times said in a report from London.
The report acknowledged that the use of English was becoming more prevalent in Friday sermons in the country but said that more research was required to assess the frequency and quality.
"The study reveals a deeply conservative body of individuals maintaining traditional languages and qualifications, and still largely recruited from the place of origin," said Professor Ron Geaves, the author of the report.
The study carried out on behalf of the BBC was aimed at gauging the ability of the clerics to adapt to the needs of modern Britain.
The clerics were 'overwhelmingly' qualified in the traditional Islamic curriculum, Geaves said, which had changed little since medieval times.
