Thanks for the info.
I've had a search for the National Union of Racing Pigeons but have turned nothing up.
The "BS" bit is the first two letters before the corrosion starts. At the end of the crroded part are the numbers 53 or possibly 55, it's very worn and dificult to tell.
The ring is Aliminium with a knurled border.
I uneartheed the ring still around the leg bone but there we're no other bones nearby. It was quite an endering find, hence my (probably overly optimistic) desire to at least try to trace the bird.