Undulating formation over sea

Hi - I've just seen a large group of brown birds - at first I thought geese - over the sea at Hove, Sussex. They were quiet, near the shore and low over the water. The standout thing was that they were in a line and in an undulating formation as they flew eastwards which would progress along the group from the bird furthest from the shore to the nearest and then repeat. It was amazing! I hope to see them again.

A quick Google tells me brown pelicans and the behaviour description is exactly right but they're found in US not UK or Europe. 

Does anyone know what they are?

Many thanks

Katie