Close encounter with a Sparrowhawk

A sparrowhawk flew within a couple of feet of me before veering off into the trees which caused much alarm from the songbirds. It seemed to be on a preysnatching course and I can only assume it knows about a nest behind the shed I was standing next to. I can't see one but I am not sure why else it was swooping down and why it didn't apparently take any notice of me until it was so close.