No interactions present.
I agree that these do look rather like robber flies, but they are in fact dance flies, family Empididae, and I'm fairly sure these are the species Empis (Kritempis) livida.
The male fly (on the right of your photo) has provided the female with a 'wedding present' of a prey item for her to feed on during mating, which can last up to 45 minutes in this species. When not mating they feed on nectar from flowers.
Entomologist and biological recorder
thanks for your help
Lat/Lng: 51.4, -2.5
OS grid ref: ST6570