Bill, the rules are the same as for all the GBs. No one seems to have come up with any definitive suggestions as to the guidelines though, so as far as I'm concerned, anything which qualifies as a Commonwealth aircraft, squadron, or Commonwealth manned aircraft, during WW2, and anything which saw service as night fighter during WW2.
Dates are from 1st November, 2010 to 28th February, 2011.