John wondered whether this might be a bird of the race known as the Baltic Gull. Our gull expert, Alan Dean, comments:
It certainly is not a Baltic Gull i.e. nominate Larus fuscus fuscus — it's nowhere near 'black' enough on the mantle (there's far too much contrast between mantle and wing-point). Also it's the wrong shape - the body is too rectangular and rear end insufficiently attenuated (the primary projection is too short). In fact, Baltic Gull is currently regarded as almost unidentifiable in the field, owing to confusion with small and very dark examples of L. fuscus intermedius. It's essential to determine the state of moult, which can be a strong indicator, but even that is not now considered diagnostic. A largish Lesser Black-backed Gull which is very dark can often be determined to intermedius, particularly if it displays just a single white mirror (on the tenth primary feather). However, John's photo doesn't look especially dark to me (particularly allowing for the exposure - the photo overall is quite dark) and is within the range of variation of the common race seen in the West Midland region - L. fuscus graellsii - which is what I think it is. All Lesser Black-backed Gull races are quite variable and in Holland, for example, there are populations intermediate between graellsii and intermedius. Thus only 'classic' intermedius can be identified with certainty (and it will probably take a colour-ringed individual to clinch nominate fuscus on current knowledge).
For more on Lesser Black-backed Gull races, see Alan's page on the species* and his picture comparing two races*.
(* WMBC reminds you that these are other organisations' sites and that the Club accepts no responsibility for their content)