Increasingly I get the feeling that cattle egrets (birds) are gradually becoming more common in the UK. Before 1955 collared doves were rare - now they are common. Before 1989 little egrets were virtually unknown here. Now they are common. Cattle egrets are being spotted regularly in Devon and I see they have been spotted up here in East Anglia.
As climate changes, the species we see will change. Changes have always happened I guess but species that hitherto have been found further south will move north.
It would not totally surprise me if some birds that winter further south decide to stay for our milder winters. When will swallows decide it is warm enough to fully over-winter? I know there are rare records of swallows staying and lasting until January living on insects near seaweed, but I don't think there are any records of swallows lasting the full winter, although I am no expert.
See https://www.rspb.org.uk/birds-and-wildlife/bird-and-wildlife-guides/bird-a-z/c/cattleegret/ .