John Holmes

The top one is a first-winter (I think) Black-tailed Gull. Features to note are: - it is medium-sized, plain coffee-coloured and the bill is slim, pink at the base with the end third black in colour.

I'd say the lower one is a first-winter Heuglin's Gull - if only because Heuglin's is our commonest big gull.  With these big gulls I recommend assuming it is a Heuglin's and then try to work out why it might be something else.  If it was paler it might be mongolicus -Yellow-legged.  If it was darker you might consider Slaty-backed Gull.

So I'd vote for Heuglin's - but I'm willing to be corrected !

John