The beach scene from Jaws was recreated near a lake or very large pond in the woods. The kids sitting round the camp fire, guitar strummer, girl and boy make eye contact, girl flirtingly runs away pursued by the boy, culminating in the grizzly discover of an arm the next day. it was in the last episode of S3. The Dirty Harry nod comes near the end as DI Thursday aims his very large revolver at the evildoer and Morse chimes in about the number of bullets remaining in the chamber, which turns out to be a bluff. There were other film references in the previous episodes but I can't recall them at the moment. Agree that there were several far fetched elements throughout the series.
Although it's a bit of a stretch, the tiger allowed some of Chief Superintendent Bright's colonial past to be introduced, tying in nicely with him being the one to unexpectedly fell the beast and heroically save the day. Previously his role has always been a bit of a killjoy stick in the mud and the plot twist served nicely to expand his character .