Is this a cattle egret? It is not in winter plumage but has a yellow bill and was among.... cattle
Yes, it most certainly is. They are beginning to colonise the UK after having spread across the world. They have bred in in several locations across Britain with the most recent being Holkham Estate in Norfolk.
https://www.birdguides.com/news/western-cattle-egret-breeds-in-norfolk-for-first-time/