If you go to RSPB website you can contact them.Click on one the top tabs and it says contact us,there will be an online form to fill in.I did this last year when I found an unidentified bird in my parents garden.
Thank you both. I think it may have been a merlin, but I've not seen one before visiting the area of our bird feeders. The "usual suspect" is more likely to be a sparrowhawk!
Not an answer to your question - but on Sunday we saw about 50 waxwings in a tree near here - NW London.
We used the RSPB guide to identify them. Twas exciting as they only get down his way every 5 or so years.
You could put it on a site eg tiny pics and then give us or anyone else the link and someone will give you the answer . I did that with an alien plant in my garden and got back an almost instant reply .