Nomia is a cosmopolitan genus of sweat bees in the family Halictidae. Many species have opalescent bands on the metasoma. Nomia species are moderate-sized bees that nest in the ground. Wikipedia
Nomia subgenus Maculonomia
Common name: Spine-thighed Forest-Nomia
Thanks for John Ascher for the ID.
Spotted at Hampstead Wetland Park