Tim Ritz has posted a rather wonderful map of British TV locations and settings on Facebook. It was posted in 2016, so there are some omissions (such as The Living and the Dead), but I have just come across it.
Wessex is represented as follows (I haven't included The Office, as Slough is historically in Buckinghamshire):
Filmed and set in Wessex
- Being Human (series 1&2)
- Father Brown
- Flowery Twats
- Inspector Morse/Lewis/Endeavour
- Lark Rise to Candleford
- Midsomer Murders
Filmed in Wessex, set elsewhere
- Downton Abbey
Set in Wessex, filmed elsewhere
- Brideshead Revisited
- The Vicar of Dibley
Obviously, this map is not complete. Can you think of any examples that may have been missed out?