Caspian-type Gull. A sub-adult, Advanced third or 4th winter type bird. A lot of black in the primaries and restricted pale tongues on inner webs- not classic features. Black extends to a band on p5. Structurally the bird looked relatively short legged and also the eye was pale. Overall a mix of characteristics with some features contra to a 'classic' bird.
Mandarin- a very rare local bird