Common Spiny-Digger

I've been trying to locate, get a shot of and identify this tiny insect for days. I thought it was some sort of diminutive Nomad bee. They are very difficult to photograph as they're always on the move and have their heads thrust into the thistle blooms all the time.

In the end I contacted the very knowledgeable @iancbeavis on Twitter, who has kindly told me that it's a digger wasp, Oxybelus uniglumis. The female digs a nest and goes off hunting for flies. She captures her prey in mid-air, stings it and flies back to her burrow with it. Between 2 and 16 paralysed flies are put in a cell and then the wasp lays eggs on them and seals the nest.