The only thing that I can think of is a scene from the LWT episode "Animals" (not to be confused with the BBC Series 8 episode of the same name).
In the LWT episode, Graeme has a pet shop. When he runs out of animals to sell he starts selling people dressed as animals as pets. Tim ends up buying Bill, who is dressed as a puppy.
This episode includes a parody of public service announcments with the theme "a puppy isn't just for Christmas, it's for life", in which we see puppy Bill with a family of small children, who initially spoil their new pet but eventually grow tired of him and mistreat him (perhaps this is what you're remembering?)
Does anyone remember the interlude? With BO pretending to be a puppy in some bluebell woodland (probably epping forest on a good day) jumping around. If you know what I'm on about, can you illuminate me as to which episode it was in or if it's available anywhere to downlaod? I haven't seen this for years so my memory could be a bit sketchy.