Having found a leaflet for a CARBRA hedge cutter that looks very similar to mine (apart from the engine), I no longer think this hedge trimmer was made by O&R. I now suspect someone has adapted it to use the O&R model 20A engine, the fuel tank fitted is from a Cox series 140 engine, same as on the engine shown on the sales leaflet.
The series 140 engine was made by O&R competitor Cox, the series 140 engine was also used on a chainsaw & bike kit and was also produced by Roper after they bought the rights to make it.
Here is the rest of the CARBRA hedge cutter leaflet scanned & converted to a pdf;
CARBRA Hedge Cutters .pdf
David