Sparrow Hawks are awesome up close OH got a picture of one that knocked a dove down in our garden then did the same as yours and sat enjoying lunch on the lawn I'll see if I can find the picture and post it..
Wow! Amazing to watch, if a little gory! We had a sparrowhawk a few weeks ago eating a pigeon in our back garden, like yours not into food waste so only the feathers were left....never did find the beak!
Wonderful to watch, though not much fun for the sparrow. What a shame there is never time or opportunity to get a photo when something like this happens.
If anything gets trapped in your greenhouse again, try going round outside to the far end from the door and looking threatening - bang on the glass even - and he will fly away from you and hopefully get out. I have had birds and bumblebees in mine, and the seem to try to go to the end where the sun shines and ignore an open door.
Flinging at him through the tiny hole though he is absolutely awesome. Barbed feathers all down his legs. He is sat on the grow bag of herbs at the moment