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Thanks, all. Dead right about unusual birds appearing just at the moment when you haven't got bins. I keep a pair in the car and one by this chair, but the little devils are usually gone by the time I pick the bins up.
This one , very obligingly, was on the drive in front of the car and flew a few yards ahead as I drove behind it'
Grey wagtails are unusual in this village, it seems. it may be that this one had come from farther afield, as Wildwood suggests, following the nearby river.