Wing colour is grey, dark hood isn't extensive and browner, beak isn't bright red so that rules out Med Gull

The hood on Ian's bird is more extensive than a typical Black Headed Gull. Kevin had a similar bird some years ago at HWR. If hybrid it doesn't look 50/50 hybrid.

Most often I hear Med Gulls before I see them.  Learn the call.  In flight they almost dazzle with their white wings and also they appear larger than Black Headed Gulls.  On the ground when walking they have a real dandy way.  

March to July is best time to see Med Gulls.  The birds come from the Belmont Colony and any sightings records after this should be treated with caution.