David makes reference to the GAMA style POH. The current revision of GAMA Spec 1 can be downloaded from the GAMA site
GAMA Technical Publications - GAMA and is worth a read for the younger set.
Prior to the original document in 1975, we had a dreadful mishmash of often not very useful manuals for light aircraft. Without digging into my really old and dusty filing cabinets to check, the first issue was very similar to an equivalent ICAO publication - can't recall at the moment which predated the other but that's probably not all that important. The document introduced a much needed change for pilot reference documents. My only hobby horse is that the weight and balance section is dreadful, but that is the prerogative of old chaps like Dave and me (I'm just slightly the more handsome but he still has his hair so I guess we're on a par).