Heartbeat is set in 1969. The most recent series have gone backwards in time! There is no continuity at all....episodes have gone from Christmas 1969 back to late August, forward to November, back to the previous February, all within four episodes!
Also a few years ago Mike was guarding a prisoner overnight and they showed him writing in the log book the date and year, 1970. This past season (or "series" as they call them in Britain) the "current" year was shown on something, a new headstone or something that would indicate the year, and it had gone backwards into the late 60's. Could possibly have been when Trish, Mike's doctor girlfriend was killed off, it may have been her headstone perhaps? I remember it because it was something "new" that would establish the "current" year and I thought it was odd that they were back in the 60's again.