Ian,
I suggest that you get in contact with your local council pest control
manager.
She/He would be able to advise and direct you towards the classic things
to do and more importantly, those which not to do.

A simple technique, which helps local bird life is to place poles (about
1 metre 50cm / 2 metres high) in the ground - in an open area. This
allows birds of prey to perch and watch the area for mice/ voles etc.
This is valuable in areas where there are few perching/observation
posts.

Only problem will be placing poison in area where raptors are working
and half dead rodents being picked up as prey!

Peter