This Common Gull deviates from the normal late winter canus with the plumage being highly dominated by juvenile feathers. This could indicate a bird belonging to a northern late breeding canus population or one could speculate whether it could be an eastern heinei but at the same time acknowledge that such identification is highly speculative without biometrics.
Features that suite heinei though without being diagnostic are:
1) long-winged appearance where the very long and slender wings are held slightly dropped on standing gull. On folded wing p5 is obviously exposed behind the longest tertials in a degree rarely mirrored by any canus and p10 is the longest primary
2) retarded moult in February with massive presence of juvenile feathers in upperparts only seen elsewhere rarely on late northern canus breeders
3) heavy markings and barring on hind neck, breast and along flanks where canus often has finer markings and a more striated patterns without the washed out appearance of this gull. Underparts heavier marked with massive barring more than on typical for canus
4) extensive bold chevrons on both upper- and under tail coverts, the rump has some dark streaking and there is barring on the outer tail feathers
5) more contrast in upper wing than on typical canus with lesser upperwing coverts darker brown than in canus and greater upperwing coverts darker brownish-tinged with weak dark subterminal spot and gradually darker towards outer coverts (most obvious in flight)
6) axillaries more barred than on typical canus
7) stronger and heavier than the average canus in direct comparison with heavy breast and beer belly in flight.
8) the bill is heavier and more parallel-edged relative to canus in direct comparison
Features not associated with heinei are the essentially sooty brown feather tips on underwing coverts where heinei are known to have paler underwing than canus and this gull actually has broader sooty brown feather edges on the underwing than canus. Photos of another similar "moult retarded" Common Gull that was seen at the same site just few days later are here and on netfugl.
Such a heavy and long-winged bird still in fresh and juvenile plumage this late in winter at least belongs to a late breeding fare northern population