Looks like a fledgling - give it some worms!
These guys are awesome - www.wras-enfieldwildlife.org.uk.
Thanks guys. We tried enfield but they are extremely busy with higher priorities understandably. We'll see how we get on with him here.
we found an injured sparrow a couple of days ago, and kept it in a box which we tied to our washing line so it was outside but protected from our cat and other predators. It didn't do much for the first day, and we thought it was going to die but after a day and a half it flew off :-)