Originally Posted by KenM
....I thought 1st Winter Mew Gulls had Barred UTC’s and much darker brown remiges or is it more advanced moult?
Mew's remiges (and tertials) usually do appear much darker than shown here, but sometimes they appear like this. Here's an example of of a similar bird (though maybe not quite as light):
I also think the exposure and lighting are playing an effect in the gull in question.