I think it's a young one - a few days ago it took a dove out of a neighbour's leylandi, and landed 10 feet away from me in my garden!  We eyeballed each other for a minute and then it took off with its dinner.  

Then last night I was watering the garden in the evening and the sparrows (15-20 of them) that roost in a large bamboo suddenly went crazy, flapping around inside the bamboo.  Then I saw why, as the sparrowhawk emerged (without one of my sparrows this time!) and took off.

That's now the third time it's hunted in or near my garden in recent weeks - I guess it's attracted to the sparrow colony.  Wonderful to witness it hunting but I hope it doesn't take too many of my precious sparrows!