I tried several times to get a wing/tail shot of this bird, and this miserable shot is the best I could do.

When I 1st saw this gull, I thought Lesser Black-back, but wasn't positive until I saw the bird flap, showing me the all-dark primaries (lacking the window shown by Herring Gulls) and contrasting white uppertail with broad black tailband. The double bar formed by the secondaries and greater coverts was also present.

In this shot the contrasty white uppertail is obvious (looking much more uniform in Herring) and though blurred, there is no indication of a light panel on the upperwing.