Bans powered
Lasham ("except on gliding business")
That's true of many gliding sites. Frequently, as at my club, it is due to planning restrictions. Many PPLs will not be familiar with gliding hazards such as 'invisible' cables on the ground or in the overhead and people on the manoevring area, so where visitors are permitted they often restrict them to pilots with gliding experience who tend to be on gliding business. Many gliding sites have relatively rough or undulating surfaces that don't have marked runways so briefings are required (think Dunstable).
P.S. Lasham does take airliners though...