I was a fan of this Canadian Cyberpunk TV series when I was young and own the first two series on DVD. One night recently watching late night TV I watched a "Max Headroom" movie. This featured the plot of the first episode of the TV series yet it featured an entirely different English cast (except Matt Frewer who played Edison Carter/Max Headroom). Why are there two versions of this story? Was it an English movie that later got adapted into a Canadian TV show?
You are correct. The movie you refer to was a British television pilot movie, intended to provide a backstory for the Max Headroom character, who presented a show called The Max Headroom Show in the style of a music video host.
The subsequent U.S. series was partially British-funded. The first few episodes of the T.V. series were essentially the film, but re-shot for a U.S. audience using U.S. actors.
Max Headroom: 20 Minutes into the Future is a 1985 cyberpunk television film created by Chrysalis Visual Programming Ltd. for Channel 4 in the UK to provide a back story for Max Headroom, a computer generated TV host. A British produced, yet American broadcast, television series, Max Headroom, was later developed from the original film. HBO provided some of the original funding.