Chelmsford 123 is a British television situation comedy produced for Channel 4 by Hat Trick Productions. It originally ran for two series, of six and seven episodes respectively, in 1988 and 1990.

The series is set in the British town of Chelmsford in the year AD 123 and concerned the power struggle between Roman governor Aulus Paulinus (Jimmy Mulville) and the British chieftain, Badvoc (Rory McGrath). Britain is a miserable place, cold and wet – just the place to exile Aulus for accidentally insulting the Emperor's horse, but it also give him something useful to do. Aulus (probably a play on Aulus Platorius Nepos, the real governor of Roman Britain between 122 and 125) is a rather delicate Roman and is usually outwitted by the scheming Badvoc, who has not had a haircut for twenty-five years. There are also appearances by many of the other regular "Hat Trick" actors, previously seen in shows such as Who Dares Wins.

Both series are available to stream on Channel 4, and have been shown in the UK on Rewind TV.

Series 1 and 2 were released on DVD by Acorn Media UK on 15 September 2011.