Can anyone identify this aircraft?

I wonder if anyone can identify the aircraft in the attached photograph. Unfortunately, I have very few details, the pilot was the Grandfather of a friend of mine and he’d love to know a bit more about the photograph.:confused:

I’ve searched through my references but to no avail, the cowl shape seems very distinctive but I think the main clue lies in the outer struts to the left of the pilot.

The writing in the bottom right hand corner says:
‘Copyright F.N. Birkett from the FNB Series of Aviators’.

Any information would be very much appreciated.:) 🙂