I think the 'minimum' to keep a licence would be a skills test with an Examiner once every two years, although this would be a rather strange way to fly!
Assuming that you are renting from a club, £200 would buy you somewhere between 2 and 3 hours, depending on where you fly (so 24-36 a year). I think most people would consider that fine, but personally I wouldn't be too happy flying much less than that.