I enquired at the British Museum regarding the tiny aluminium tag I found:
One of the BM staff soon emailed to let me know the following:
“Thank you for your enquiry. It looks like you have found a pigeon tag. These have no connection to the activities of the British Museum, even though its name appears on them.
There is a website providing a list of contacts for lost racing birds, which includes details of who to contact in the event of finding a ‘British Museum’ tagged bird: http://www.birdman.co.uk/Stray_Birds.htm.”
So the mystery is solved. I do wonder if my pigeon perished in that field though.
I’ve just had (7 April 2015) a further update from a different department of the British Museum. Virginia Smithson of the Department of Britain, Europe and Prehistory, has written and passed along a link to a description of bird ringing activities in Britain. This information can be found on the target page:
Why are there some rings with Brit Museum on them?
Historically, the British Trust for Ornithology has used the address Brit Museum NH, London, SW7. This refers to the Natural History Museum in South Kensington, London and not the British Museum, which does not have any involvement in bird-ringing. This address was used because the words London and Museum are easily recognisable, even to those who do not speak English.