No idea of the system now but back in the 70s we had a number of low level flying areas, (North Yorks Moors was one) and also a low level route which as I recall went round the whole of the British mainland - always flown clockwise. That way everybody shared in the fun - not just the Welsh!
Remember taking Mrs TTN to Aysgarth Falls (I think) which was a turning point on the route, when we were on holiday in Yorks. After a while she commented that there seemed to be a lot of aircraft around, as a succession of Vulcans, JPs, Buccs etc passed overhead at about 5 minute intervals. I replied that it must be a coincidence!