The film was shot over 28 consecutive days, during July/August 2001.
The film spent three years in development hell. It was originally scheduled to be filmed in September 1999 but funding fell through and it was re-scheduled for summer 2000. Once again funding fell through so it was shelved until 2001 when the director decided to partly fund it himself with the help of other film funding sources in Cornwall and it was finally shot summer 2001. It was released a year later.
Through out filming so many things went wrong (boom problems, camera, sound problems), the producer tried to lighten the mood by bringing in copies of the film Living In Oblivion by Tom DiCillo and distributing them through out the cast and crew, instructing them that it was a "self help" guide to making a film. Later director Antal Kovacs would refer to Hwerow Hweg as the living proof of Living in Oblivion.
In the original draft the end involved a long car chase with Jack eventually catching up with Becky on a beach, raping and murdering her, then driving his car back to his bedsit where he had built a secret shrine. Unfortunately due to budget and other problems with censorship the final scene was completely re written. Instead a scene having Jack attacking Becky was added in the middle to help with the explanation of Becky's hatred for Jack.
Hwerow Hweg wasn't originally going to be made as a Cornish language film. It went through several names: Kill The Bitch, Robert 4 Helen before it was finally titled as Bitter Sweet. The producers made the decision for it to be shot in Cornish came about from the directors interest in the language.