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

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

Both series are now available on 4 on Demand and SeeSaw.

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