Turkey's most important Islamic network, the Gulen movement, helped bring the ruling AK Party to power in 2002. But now it threatens to bring it down. Fethullah Gulen, the reclusive Muslim cleric who leads the movement, has hinted that he believes the AKP is no longer fit to govern.

Presenter Edward Stourton travelled to Turkey to investigate the Gulen movement in 2011. He discovered unease amongst the Gulen's critics about the movement's influence in key institutions, including the police and judiciary. In the wake of the recent power struggle between the police and the government, he examines the Gulen's role in the rift.

Producer: Helen Grady.