An Oxford University Islamic scholar who advised the British government faces a second rape investigation, Swiss prosecutors have announced.

Tariq Ramadan, one of European Islam's best-known figures, was detained in France earlier this year over rape allegations by four women.

Prosecutors in Geneva, Switzerland, have now disclosed that they have opened a rape and sexual misconduct investigation against the married father of four.

Islamic scholar Tariq Ramadan faces a second rape investigation, this time in Switzerland

Ramadan was previously one of British Foreign Office’s Advisory Group on Freedom of Religion or Belief.

He was a Professor of Contemporary Islamic Studies at Oxford University, and was a member of a taskforce set up by Tony Blair after 7/7.

The 56-year-old, who has multiple sclerosis, is being held in a prison hospital in Fresnes, south of Paris.

The Swiss citizen, whose grandfather founded Egypt's Muslim Brotherhood movement, took leave from his post at Oxford University after the first set of allegations surfaced.

Geneva's prosecutor's office spokesman Henri Della Casa said authorities are investigating allegations that Ramadan raped a woman in a Geneva hotel in 2008, according to The Tribune de Geneve newspaper.

'I confirm the opening of an inquiry,' the paper quoted Della Casa as saying, a key step that indicated the authorities believed the allegations merit further investigation.

The accuser lodged her complaint in April.

Ramadan was a Professor of Contemporary Islamic Studies at Oxford University (pictured in a file photo). He took leave from his post after the first set of allegations surfaced

'The prosecutors and Geneva police have worked quickly and worked well,' Romain Jordan, the lawyer representing Ramadan's Swiss accuser, told AFP in an email.

He described the decision to open a criminal inquiry as 'a major advance' that 'demonstrates the seriousness of the allegations made by our client.'

Ramadan has not yet been interviewed by Swiss prosecutors, who will now have to travel to France to interview him.

The 56-year-old scholar, a prominent and controversial figure within Islam, has denied any criminal wrongdoing.

On Tuesday, Ramadan will be questioned in the presence of a second accuser, a disabled woman identified as 'Christelle' who claims he raped and beat her in a hotel in the southeastern French city of Lyon in 2009.

Ramadan has denied wrongdoing and is suing one of his accusers for slander.