He's been called the government's "real Mr Brexit", but is little known outside Whitehall. Mark Coles asks who is Oliver Robbins, the Prime Minister's right hand man for the Brexit negotiations? In the last few months Robbins' role has grown, taking the lead on negotiations with Brussels often without the Brexit Secretary, David Davis. This has led some to question whether a senior civil servant should be given so much power.

He had a meteoric rise, becoming Tony Blair's Principal Private Secretary, the most senior civil servant at Number 10, aged only 31. He is almost universally admired by those who've come across him for being able to distil huge amounts of information quickly, keeping calm under pressure, and having a sense of humour. He is popular in Brussels, where his interlocutors appreciate that he is straight with them, and that he "doesn't lie". The consummate mandarin and public servant, not even long-term friends know where he actually stands on politics or Brexit. And he's managed to keep a low profile, despite his role.

Producer: Arlene Gregorius.