The RMT union claims to be Britain's fastest-growing trade union; it is also arguably the most confrontational. The union's favoured tactic of repeated strike ballots has won enviable high rates of pay and annual leave for its members. It has also earned the RMT general secretary the tag of 'the most hated man in London'. Simon Cox investigates the RMT's strength, why managers refuse to take it on and the attempts to curb its power.