First Secretary of State, Damian Green, is under mounting pressure this week due to allegations of improper behaviour, and claims that pornography was found on a computer in his office back in 2008 - allegations he staunchly denies. Sue Gray, Head of Propriety and Ethics at the Cabinet Office, is leading the inquiry into whether he broke any rules.

Gray has been described as "the most powerful person you've never heard of". Mark Coles finds out more about the woman who joined the civil service straight from school, and has risen to occupy a pivotal position right at the heart of government.

Presenter: Mark Coles Producer: Beth Sagar-Fenton.