He's long been one of the most powerful figures in British government, but few outside Whitehall have heard of him. The next Cabinet Secretary Jeremy Heywood has been at the centre of British government for two decades. He's been close to top politicians ranging from Norman Lamont to Tony Blair to David Cameron. And he's been in the thick of controversial episodes such as Black Wednesday, rows within the Brown government, and the global financial crisis. So what's the secret behind the huge influence of a man who shuns the limelight? Chris Bowlby profiles "the insider's insider".Producer: Smita Patel.