Univoltine, but with an extended flight period. Females fly from late March to the end of October, males from late June to late October (exceptionally early November). The species may be bivoltine as R.C.L. Perkins (G.M. Spooner, pers. comm.) reported "a colony in a Paignton [Devon] garden produced males and females in June: these females paired and provisioned cells, and gave a second brood in August".
Label data from a few Spanish specimens (and one from Gibraltar) shows that females are active from June to August, and the males from June to October in Iberia (Ortiz-Sanchez & Pauly, 2017).
Parasites G.H.L. Dicker has observed S. niger around the nests of this species in Kent, and I have seen the same Sphecodes flying over a nesting site of the same species on the Isle of Wight. S.P.M. Roberts made similar observations in Middlesex, Wiltshire and in Oxfordshire.
In Germany, Westrich (1989) records Sphecodes geoffrellus, S. niger, and Nomada furva as possible cleptoparasites of this species; Alfken (1913) additionally lists S. miniatus.