Why does the Robin in my garden have a ring on its leg?

Here you go Rachel, this may give you the information you need.    

Some bird reserves carry out ringing by licensed "ringers"         If you manage to get enough photos of the ring it will have a series of 7  letters/digits  which you can then forward via THIS WEBSITE and you will receive back information on that particular bird.   You will need all of the leg ring code before you can report it.      All the data gained from recapturing birds is invaluable to the monitoring of birds, their movements, age, location it was ringed,  etc...….    If you get a chance to see a ringing session  (some reserves have special days when you can view the birds being ringed and BTO (British Trust for Ornithology) have ringing sessions during the annual BirdFair  held at Rutland each August   (maybe not this year due to Coronavirus)       It is worth seeing the process as it will confirm that the birds are not harmed in any way and the ringers are extremely well trained and professional -   they can only carry out ringing after years of training.

I should have mentioned that all ringing is suspended at the moment and reserves closed due to Covid-19