The Avro Trainer is most likely to have been an Avro 504. These were fitted with a variety of engines, so the 'Leabone' may in fact be 'Le Rhône', to differentiate it from the Gnome or Clerget powered 504.
From the Coates Collection
Avro 504K B7103:
Avro 504Ks were fitted with one of about ten different engines and hence, just by looking at it, one cannot tell what powered D7103. It was probably a 110 hp Le Rhone rotary. An incredible 8,340 of all versions of the Avro 504 were built, of which the most numerous was the 504K. They were still being used by the RAF as trainers as late as 1933.
Leighterton is in Gloucestershire. More info here:
http://www.airfieldinformationexchan...68-Leighterton
An aerial view can be found here, as can pictures of a couple of bent 504s at Leighterton:
http://www.awm.gov.au/collection/P00048.019