Taken at Titchwell, I thought it was a female Reed Bunting but the stripe over the eye doesn't appear in my books. thanks, David
https://www.youtube.com/watch?v=INNTOEL1oic
I think that the flaw is in your book, not in your judgement. I found several images online that show a definite eye stripe, including this.
Our herring gulls are red listed birds. Think about that the next time you hear some flaming idiot calling for a cull of them.