PYRTLE
Old Berkshire Boy
I'm sure your correct with the identification though the behaviour you describe is more reminiscencet of Hobby hunting tactic, particularly seeking out hirindines.....swooping and chasing then climbing sharply and high to seek out another target. Mind you, I've seen an adult female Sparrowhawk repeatedly and successfully catching Sand Martins gathering in the Autumn, albeit typically an ambush stratergy from the same hidden vantage point.