Maskell's first television appearance was in 1991 in the ITV police drama The Bill. Between 1992 and 2002, he made a further five appearances on the show, portraying a different character each time. He has had one-off roles in a number of other popular British serial dramas such as Casualty, London's Burning, Soldier Soldier. His most regular television roles have been in the 2005 comedy series Mike Bassett: Manager, in the comedy Sketch show The Wrong Door, and in the 2013–2014 thriller drama action series Utopia. Since 2015, he has been a series regular in sci-fi thriller Humans.