its a good point - I have recently waded through all the Heartbeat episodes having started watching early last year and finished when they reached the end about 3 weeks ago. They did try to be fairly accurate -but as the 60s progressed the appearance of steam locomotives towards the end was anachronistic as some of the cars had 1969 tax disks and I spotted one car with a 1970 suffix. However, some of the road vehicles were suitably rough at times and they certainly must have crashed a few classic cars for a bit of realism as I suspect a few prangs were not trick filming though it is obvious some where. Thus the likes of Heartbeat I would give about 7.5 / 10.
Moving on to more recent crime dramas Endeavour (Morse) doesn't do a bad job on the 60s - but Father Browne and the new spin off Sister Boniface have plenty of anachronisms not just in terms of how they look but also the dialogue
The episode of Sister Boniface last night had the two policemen sat in a car listening to a bug through head phones - which looked rather like ones I saw in a pop up advert on Facebook a few days ago.

Back in the 1970s I was in my school CCF and we had a few army radios. What I recall of the headphones were they were much more primitive and probably the police in Sister Boniface should have been using something along that design being government issue. At present I think Father Brown / Sister Boniface would come in at 5/10 and 4/10- for period realism.
Some might say it doesn't matter as its just a drama - but I think it does matter I do like to see a lot of effort put in to get period things correct. Foyles War was spot on and I watched that with my mother at the time. She was often critical of period dramas depicting the "home front" having lived through the war years. She thought Foyle to be fairly spot on.