An interesting Gull?

Whilst walking along Pagham Beach this afternoon I came across this gull feeding alongside several Black Headed and Mediterranean Gull. Its mantle was obviously  very pale and but the ear coverts and wing tips were 'normal'. I deduced this was an instance of leucism as in every other aspect it was very much a Black Headed Gull. I have not seen this bird before and don't recall any other reports. Any comments would be of interest.

Conditions were not good for photography as it was very foggy in the late afternoon but these shots taken on my compact camera give a reasonable record.