Good luck with this one, Dave. I gave up on this 25 years ago. I'm sure the film still exists but it would look pretty weird seeing it on ANY TV channel (including movie channels) and is unlikely to receive much public interest. That's based on similarly obscure and forgotten gems from well-known actors that have eluded me for years. Glenda Jackson in Negatives, for instance. Or Rita Tushingham in The Girl With Green Eyes.
As I'm sure you know, Albert Finney and Rachel Roberts also starred together, much earlier, in the classic film Saturday Night And Sunday Morning, which has recently had an exciting DVD release (digitally restored, extras). It would have been even better if Alpha Beta was included as a bonus. A lost opportunity or a rights issue? Either way I'd love to see it myself.