UK companies are being used to launder dirty money as new transparency rules are flouted. One, registered in a Hertfordshire commuter town, helped the circle of Ukraine's disgraced ex-president profit from last year's Eurovision Song Contest, a File on 4 investigation has found. Billions of pounds of dirty money is alleged to have passed through opaque UK companies in recent years, over 100 of them registered at the same Potters Bar address. Tim Whewell follows the trail of one company linked to the regime of former Ukrainian president Viktor Yanukovych, who fled the country for Russia four years ago after anti-corruption protests in Kiev's Maidan square. Can new transparency requirements for British firms help find the people really behind the company? Presenter: Tim Whewell Producer: Simon Maybin Editor: Gail Champion.