I've also received a few comments about the Whitby bird of I think 2000/01. The important difference between these birds is that the Barmston bird has an even dark shaded area adjacent to the shaft streak the whole length of the feather on both webs of every primary . The Whitby bird in contrast has a faint shaded area on the outer web of the inner primaries and a complex subterminal mark on each feather, but the dark decreases on the outer feathers. The Whitby bird appears to just be an unusually dark pigmented bird and the dark marking in the primaries are merely an extension of the dark marks on the secondaries and inner primaries.
The Whitby Gulls wing
a similar [although with pale not dark pigment] phenomenon is seen in 1st winter birds often claimed as Glauc x Herring hybrids that in reality are just argentatus Herring gulls at the pale end of the spectrum where the pattern on the inner primaries extends further on to the outers giving a paler appearance and inviting the conclusion that there is Glauc influence. This is illustrated in the pic below