Falco tinnunculus. See http://www.rspb.org.uk/birds/guide/k/kestrel/index.asp

The Kestrel had just caught something small and furry by Dudingston Loch, and obligingly sat in the tree eating while I got the scope and camera on it. I got a few photographs of it at that point, but nothing worth publishing. However the shot that I wish I'd got was when a Blue Tit flew into the tree just behind the Kestrel. It looked over the Kestrels shoulder at what it was doing to the small furry animal - with an expression that just said "GROSS !".