These birds are getting more common in the UK. They have yellow beaks unlike little egrets that have black beaks.
This is probably due to climate change. Another 20 years and they will probably be common.
At the moment there are cattle egrets 2 miles from where we are staying in Devon, although I have not seen them. Well, I may have, but the one I saw was too far away to ID positively, although it was very close to a cow.
See https://www.rspb.org.uk/birds-and-wildlife/bird-and-wildlife-guides/bird-a-z/c/cattleegret/ .