Dilpazier Aslam, who has been allowed to report on the London bombings from Leeds and was also given space to write a column in last Wednesday's edition of The Guardian, is a member of Hizb ut-Tahrir, a radical world organisation which seeks to form a global Islamic state regulated by sharia law.
It is understood that staff at The Guardian were unaware that Mr Aslam was a member of Hizb ut-Tahrir until allegations surfaced on "The Daily Ablution", a blog run by Scott Burgess. Speculation is mounting that it may have been a sting by Hizb ut-Tahrir to infiltrate the mainstream media.
Late on Friday The Guardian released a statement to The Independent on Sunday saying: "Dilpazier Aslam is a member of Hizb ut-Tahrir, an organisation which is legal in this country. We are keeping the matter under review." The paper refused to comment further.
In 2001 Mr Aslam wrote in the group's in-house journal, Khilafah, that: "The establishment of Khilafah [an Islamic state] is our only solution, to fight fire with fire, the state of Israel versus the Khilafah State".
The day after it was revealed that the London bombers were British, Mr Aslam wrote a column in which he billed himself as "a Yorkshire lad born and bred".
In the piece, he suggested that second- and third-generation British Muslims were prepared to "rock the boat" and that agitation against British foreign policy would build up "till it can be contained no more".
At the end of the piece readers were not told that Mr Aslam was a member of Hizb ut-Tahrir, only that he was a "trainee journalist". Though Hizb ut-Tahrir is a legal organisation in this country, the group is outlawed in nearly every other country it operates in, including Germany and Holland. It is thought to have between 2,000 and 3,000 members in the UK.
Speaking for the Muslim Council of Britain, Mr Inayat Bunglawala said: "For a party which claims it is open, you'd think this person would have disclosed his affiliations."
Mr Bunglawala added: "The Guardian has a better record in giving space to minority voices but [by employing a Hizb ut-Tahrir member] it exacerbates the idea that this is a mainstream Muslim voice," he added.
Sources in The Guardian said that Mr Aslam was employed to increase ethnic diversity within the newsroom under The Guardian's one-year traineeship scheme.
One source said: "There was a feeling that we genuinely wanted more diversity, and like all national newspapers we were still a bit 'pale and male' so we were keen to recruit from different backgrounds."
In 1994 Richard Gott, a veteran Guardian journalist, resigned as literary editor after he was unmasked as a former KGB spy. He admitted meeting the Russians and going on expenses-paid trips, but denied taking money. Last night The Independent on Sunday was unable to contact Mr Aslam for comment.