I've just completed an online jigsaw puzzle which featured this lovely bird. It's very obviously not a gull:
The beak reminds me of an albatross so perhaps it's a related bird.
All help most appreciated!
Our herring gulls are red listed birds. Think about that the next time you hear some flaming idiot calling for a cull of them.
For advice about Birding, Identification,field guides, binoculars, scopes, tripods, etc - put 'Birding Tips' into the search box
I've never seen one but this site :
https://animaldiversity.org/accounts/Fregata_magnificens/
says the juveniles have white heads.