No interactions present.
Yes to Megachile, but difficult to say which species. Really need to see details of the hair-colours on various parts of the body, including the underside, and posibly a close-up of the mandibles as well. There's a key to leaf-cutter bees in British Wildlife magazine (vol. 10 part 6, 1999).
Entomologist and biological recorder
Lat/Lng: 51.7, -2.6
OS grid ref: SO6208