Well, if the herring gull is on the "red" list for the UK, I can tell you were to find them - in the towns on the Yorkshire coast. In mine they've chased out black-headed gulls, and we rarely see a common gull or a tern. And what, exactly, are Mediterranean gulls doing in the UK in any case??
When we first moved here over 30 years ago there was a nesting pair of herring gulls about a mile away on the main shopping street. Now every double-chimney of six pots on terraced houses built around WW1 has a pair.
Over the last five years they've opened up a second front on the top of flat-roofed dormers. It hasn't taken long as each pair raise 2-3 chicks. When they set up an alarm call you can hardly hear yourself think. Even the tree-nesting crows are moving out.
Don't you have them in The Netherlands?? Can we send you some??
Please?!