I remember when we sold a K7 to a couple of guys from (I think) Kenley. They came up to Newark to test fly it and it was a glorious day. They kept asking us if it was OK to thermal above 2,000.......
If I remember correctly the Cadet Force gliders at RAF Sealand were limited to 2,000 due to proximity to Speke. Or John Lennon I should say. Mind you they flew barges, I would imagine 2,000 feet in one of those would be a champagne popping event.