Do kestrels eat fish?

 Yesterday we were walking along the path by the river Deben in Suffolk. It is river on one side and low lying grazing land on the other. 
A bird of prey was looking for food over the field. Can you confirm this is a kestrel please?

it was unsuccessful over the field so switched to the river where it again stopped mid flight before diving into a small group of sea birds sat on the river. The birds were highly alarmed and flew off but the bird had caught something.

has it caught a bird or a fish?

Do kestrels eat fish?