We're pretty sure this is a female grey wagtail in summer plumage, although she doesn't seem to have as long a white stripe above her eye as the pictures in the books suggest. So if anyone knows better, please let me know!
We spotted her carrying this tasty morsel whilst visiting Quarry Bank National Trust property at Styal, Cheshire, to which we took Mum-in-Law for a day out from her care home. It's well worth a visit as the cotton mill machinery is fascinating, and can be seen in action. I took some photos of that too, but the wagtail won today's blip.
We'll probably go back to Quarry Mill in about a year's time as they're currently working on some new exhibits.