Odd herring gull: double thayeri on right wing

These Lesser Black-backed Gulls have never seen a Herring Gull looking like this before - well, at least I haven't! This Herring Gull seen at Alnwickhill during a brief visit today showed an extensive white tongue on the primary 9 reaching all the way to the white mirror at the tip (this is the thayeri pattern as it is the pattern shown typically by Thayer's Gulls). Very unusually, this bird repeats the pattern on P7, on its right wing at least. It also only had one leg, had a fairly pale yellow beak for an adult bird and appeared to have very oddly bulging central primaries (or maybe it has just moulted P1 and P2). Altogether a pretty unique looking bird!...