Almost exactly three years ago, Tom Watson stood up in parliament and demanded the Metropolitan police investigate ‘clear intelligence suggesting a powerful paedophile network linked to Parliament and No. 10’. It was an incendiary claim which, because it was made during Prime Minister’s Questions and broadcast on live television, set hares running on social media and beyond. We know, now, that the police found no evidence to support an allegation of rape made against Leon Brittan by a woman known as ‘Jane’. But the question remains: what about that link to No. 10? I have spent much of the past three years looking into this. Working for BBC Panorama means following the evidence — no matter how tough and painful the process.