A magpie mugging a kestrel?

In the car when I saw this kestrel hovering . As I watched the magpie came into the scene - am unsure if the kestrel (at the bottom of shot) was swooping on prey or if the magpie was a threat to the kestrel itself - the magpie did have a close encounter with thekestrel which then moved across the fields to hunt.

Not the best of pics but it was a bit away from me and I stayed inside the car so as to not interfere.