Have you told them limited milage? could you register it at a different address? That would come down a lot if it was parked in a garage or on a drive.
I have the same problem every year, put a-plan or K.M have always been the cheapest(last 3-4 renewals). Have you joined an owners club? they often get discounts with certain company's.
Greenlight is no good as my car is on their excluded vehicle list