I have had this response about the gull from a man who knows and I am sure he won't mind me putting it here!
'The other bird is a 3rd-w Herring. The white tips to the primaries confirm that it is a 3rd-w and the extent and pattern of brown in the tertials and coverts is typical of Herring and would be extremely unusual in Caspian or Y-l Gull at this age. Basically at this age many Herring Gulls appear about a year behind on their upperpart pattern. So, a Caspian showing this extent of dark in the coverts and tertials would be a 2nd-w (and the brown would tend to be darker and more solid in the tertials and it would show no white primary tips). A 3rd-w Caspian with white in the primary tips would typically appear much more adult like in the upperparts, with any retained dark markings in the tertials still blacker than Herring. ' - Thanks Mr R
Thanks for the response Ben, I am still baffled by large gulls!!