if you look at the bird's mantle (back) you can see some new grey feathers moulting in. The tone of these is much paler than you'd see on a GBBGull. There are also some structural features that point away from GBBGull but they'd bore the .... off a beginner to gull ID I feel! If you go back to a field guide with those mantle feathers in mind, the id will be much easier. If not, I'm sure someone will come along and name the species.
I'm rubbish at gulls too, but I reckon this is a Herring Gull. Structurally wrong for a GBbG (especially that bill), not nearly scary enough, and it's grown a few adult-type pale grey mantle feathers.
All the best from the other end of Hants.
Ditto to Herring Gull
Agree with the others Peter; plumage aside (and I am a self confessed "non-gull" birder) the sheer size of GB-bG and the ultra-heavy bill makes it stand out.
This one is standing in front of a Yellow-legged Gull which has a very similar structure and bill size to your bird:
Thank you all for your replies - I told you I was hopeless with gulls (particularly juveniles).
Forktail and Steve, yes, I had missed the grey feathers emerging on the mantle.
Thanks for you image Colin. Yours would have thrown me too. A trick of the lighting I know but it has a pink leg and a grey leg
PS: I have changed the title, now I need a .
I'd have said 2nd winter, not 3rd.Herring Gull as said, a 3cy type.