Hello,
I agree with you and Jon, its a 2cy Yellow legged Gull (if taken recently).
The obvious moult gap in the wings is bad for a juvenile bird in september. Otherwise, impression of the dark mask around the eye (too much mascara for saturday night?) extensive barred axillaries and large dark areas on underwing and weak, but just notable pale inner primary window seems good for a YLG.
But you know, I am regular grateful surprised by correction!