2017 hasn't really got going yet for me. So here's a photo of a bee from last year. It is here so I can link to it from another ID site that seems to have various size and format limits. I think it may be a cuckoo bee so any views on this will be gratefully received.
Longish abdomen, yellow on the flanks, no pollen, possibly Gypsy Cuckoo Bee or Vestal Cuckoo Bee?
Update:
This has been confirmed as a Cuckoo Bee, either Vestal or Gypsy. In which case I probably saw quite a lot of these last summer. There are various explanations of things to look for including both anatomical features and behaviour, but for me the abdomen seemed quite long and distinctive.