As one of the glider pilots at North Weald and Ridgewell (and I sometimes visit Dunstable and Halton), where we fly up to the base of CAS, the last thing we want is that base being lowered to give 1000 feet of clearance. We have no problem with 500 feet. In practice, I have never known an airliner to be at only 500 feet above CAS base directly overhead because it would have to be right in the corner of CAS to do so at North Weald or Ridgewell. If that were to happen, I would not consider it to be a problem, but we would probably want to avoid the immediate area for a while to avoid the wake. We could live with that. I hope Slaphead and others would confirm if asked that airspace busts in Stansted and Luton CAS are rarely by gliders - for some reason, it seems to me that PPLs are the vast majority of such busts.