Line of Duty's Martin Compston addresses fan criticism of final episode Martin Compston, who plays Steve Arnott, wrote a message to fans on social media Updated Line of Duty's Martin Compston has addressed criticism of the series finale which saw H unmasked. During Sunday night's episode of the BBC One series, DSU Ian Buckells, played by Nigel Boyle, was unmasked as the mysterious H, the corrupt police officer at the top of a criminal conspiracy. The much-anticipated episode was watched by an average of 12.8 million people, with a 56.2% share in overnight viewing figures, making it the most...