Looks like Mock Orange aka Philadelphus snowbelle.

Could it be a Deutzia? It's very pretty whatever it is.

I was going to say philadelphus too

I think it might be a Deutzia "Pride of Rochester." It is a beauty whatever it is. Ooops! seem to have added this twice.

I'd say Deutzia, too, as the flowers hang down. Philadelphus flowers tend to be upright.

first thought is deutzia, going by the bud case.

Difficult to tell form the pic, but the leaves on Deutzia tend to be more elongated and thin. Mock Orange has slightly rounder leaves.

Either way it looks like Nightjar has a nice healthy looking shrub.

thank you all for answering my question -and having now looked in the wifes flower book we are sure its a deutzia.
dave.