In the end, I bought it home. Did a quick bit of research on the net and popped it in our downstairs bathroom with food and water. It seemed to be in a bit of shock, but within a couple of hours was hopping around a little in there having a bit to eat and drink.
This morning, I was just trying to work out who to call about it when I checked in. Crow looked like a whole new bird, I popped it outside and after it'd got its bearings it went on its way.

Now I'm not completely sure I did the right thing, maybe I should have left it in the park. But I couldn't bear the thought of one of the dogs getting it or a cat during the night. I do wish I'd taken a photo before it went though.