There's a couple of aviation fora with more details on this (pprune being one, can't remember the other) - one of the pilots involved has apologised and given some background: gliding event was a junior competition at Bicester (so many pilots relatively inexperienced), and the organisers, despite being aware of the restriction zone around the Reds, changed the route at the last minute (due to weather), placing a turning point only 200m from the restricted area. Over 20 gliders (from a field of 44) ended up infringing, and have apparently reported to the CAA. Personally I'd hold the organisers at least as culpable as the pilots on this one.