Tough question to answer, so many factors involved. Are we talking day or night, from 500' or 20,000', do you want the whole of Leicestershire in focus or just a particular building? Are you moving or hovering?
To start with I'd recommend using aperture priority and letting the camera work the rest out. If you go around f8 on a nice sunny day that should give you a good semi fast exposure. Rule of thumb on a full frame camera is set the speed to match the focal length, so a 400mm lens for example you'll be at 1/400.