It occured to me that to get the proper British countryside feeling right, Sir, You Are Being Hunted is gonna have to get rain right.
Few games do this. Even the XRay engine for Stalker had pretty crap rain...
The only game that comes straight to mind is Morrowind. Something about the audio for the rain and the fog effects along the Balmora coast that got it really right. There was something about that kind of dull, gently oppressive rain along that coast was really evocative.
Any other suggestions of games that have done rain well?