If your not use to english countryside take a long walk in the various seasons, crop and terrain varies from month to month, august it could be hard groun and stubble, september it could be ploughed and soft, terrain can also be deceptive. Get yourself some boots and take a long walk, as you walk across fields, consider ther merits, winter everthing gets a bit soogy and soft. I have to say that from my experience, with students and skill test candidates, with a background in agriculture or gliding usually perform the best, in field selection, but it's not an exact science. On the other hand there are hundreds of disused airfileds in the UK which you should consider, if there within range