The rather blunt end to the abdomen and the absence of post-spiracular bristles excludes Aedes and Ochlerotatus. Your thorax picture shows the prespiracular bristles very clearly, and combined with the banded tarsi indicate Culiseta. The dark spots on the wings combined with the subapical ring on the femora take us to annulata/subochracea. Finally the clearly marked pale basal rings on the tergites suggest annulata.
Doh! Inexplicable user error. I noted the post-spiracular bristles weren't present then for some unknown reason went off down the other side of the key.
Thanks for the correction and explanation Tony. When you say 'suggest' does that mean the images don't give you enough confidence in that final choice for a record?
That's nought out of two for me keying mosquitoes so far but I'll keep trying. I'm using the RES key IX, pt2, 1950. Is there anything more recent?
I'm a bit wary of IDing anything with certainty from a photo, but in this case, I'd say the ID is almost certainly OK - partly a function of it being a very common, widespread and distinctive species. Having said that, there have been quite a few additions to the British list in recent years, so it's as well not to take anything for granted.
Cranston, Ramsdale, Snow and White 1987 Adults larvae and pupae of British mosquitoes (FBA Scientific Publication no. 48) - See Pemberley Books (£13) - covers most of the species.