Richard Bonser has very kindly emailed me these images taken of adult AZOREAN ATLANTIC GULLS in the Azorean archipelago in November.
These three individuals show how variable the head streaking can be. You can see the rather heavy appearance of this species with proportionally shorter legs than michahellis, and the much paler iris than a typical michahellis. There is a substantial amount of black in the outer primaries, more so than in michahellis (though P4 is meant to often show a subterminal band but obviously there's no spread wing shots here). Also interesting to note how dark the mantle colour is compared to the LBB Gull in the lower shot.
The current Bedfordshire bird does share some of the characteristics apparent in these images, although the leg colour is very different (much duller).