A new one on me when I first saw it a month ago, this is one of the most colourful insects I've ever seen. it looks like it belongs in the tropics rather than the U.K. and indeed they mainly fly in the hottest and driest months of the summer and really prefer a Mediterranean or Sub-Tropical climate.
Since seeing it I've researched and found that it parasitises both the Mason and Leaf Cutter Bees, both of which are solitary bees that make their nests in holes created by wood-boring beetles or alternatively in hollow reeds. The Mason Bee creates cells using mud and the Leaf Cutter makes paper maché from the leaves it cuts. The Cuckoo wasp lays its eggs in the host's nest and its larvae consume first the larvae of the host and then the food supplies laid down by the host for its young. I have never heard of the hosts taking action against the parasite but in filming I came across the event that I managed to film. I've taken liberties with the sound track to help dramatise the scene but if it offends please mute the track. Thanks.
Yet another great piece of film John.