I photographed this gull in a small park in the Clifton area of Bristol last week. Unfortunately I only had a short lens with me and the bird flew away as soon as it realised it was under observation!
I assume that this bird is a LBBG x HG hybrid. The bird's mantle shade was between LBBG and HG but was probably closer to LBBG. Its legs were yellow, but perhaps not as bright as a classic LBBG. In flight clearly only one mirror on p10 visible both above and below. Clear white tips on p5-9; band on p5 narrow. One feature that seems unusual are the strong white moons on p7-8. Any comments? Apologies for the poor pics.