David Cameron insisted police and ministers had “serious questions” to answer today after one of his frontbench spokesmen was arrested over Home Office leaks.

The Tory leader hit out after shadow immigration minister Damian Green was held in custody for nine hours last night as part of a Scotland Yard investigation.

Green’s arrest follows the launch of a molehunt in the Home Office, ordered by senior civil servants in the department after a series of embarrassing stories appeared in the press over the past year. It is understood that ministers played no part in initiating the investigation.