Thanks again to all of you for help with this one. I had my test on Sunday and passed. I diverted to an airfield 22nm from my position and arrived almost dead on time (-10s). The chosen method was the cardinal points with drift and ground speed. It is straightforward enough to estimate a drift and g/s from these points and work out the ETA. The other methods sound useful also which means I can now try them without the pressure of an examiner !
Cheers guys