Iran's leading ideological dissident, Abdul Karim Soroush, has had his passport confiscated by the Iranian intelligence ministry and been prevented from attending a conference in Britain.

The action was disclosed in a letter from Professor Soroush to St Anthony's College, Oxford.

The move against the popular Tehran academic is being seen as part of a campaign in recent weeks by conservative hardline clerics in the government and Parliament to thwart the incoming administration of the president-elect, Mohammed Khatami.

Prof. Soroush has been banned from teaching at the university for the past 18 months. He has been the leading exponent of the view that the clergy should restrict themselves to offering spiritual guidelines and not become involved in politics.

Mr Khatami was voted in last May by an overwhelming mandate from young people and women seeking more freedom in social life and expression. He is due to take office in three weeks.

The fate of Prof. Soroush and the imprisoned writer Faraj Sarkuhi, who faces charges of espionage, depends on the outcome of the struggle between the conservative faction and the incoming liberals.

Mr Khatami is trying to put together a cabinet which would remove key hardliners from power. They include the feared information minister, Ali Fallahian, named in the recent Berlin trials as the main organiser of the killings of three Iranian dissidents.

The debate has exacerbated existing divisions within the clergy. Even the grand ayatollahs and such powerful institutions as Qom Seminary Teachers Associations are arguing about whether the 18-year-old Islamic revolution should reform itself and liberalise.

The day after Mr Khatami's victory, Grand Ayatollah Montazeri issued a letter congratulating the president-elect and urging him to protect human rights, freedom of the press and association, and social liberties.

The debate has also infected other conservative power bases under the control of the supreme leader, Ayatollah Khamenei, who is believed to support the conservatives.

The most important is the million-strong Bassiji force, the volunteer squad which formed the suicide battalions in the Iran-Iraq war. They are now deployed in maintaining Islamic behaviour and dress in public, a role which Mr Khatami wants to lesson.