[Lynn Eades]

In saying all that, for Dan's benefit, The relatively low compression ratios of most war time engines was in the area of 5 or 6 to 1. This in most cases would have been pretty forgiving except that (as per Tony's post) most British vehicles had a very low power to weight ratio.(iets say a conservative approach to horse power)
Nowadays Dan, most European and Asian built cars are running about a 10 to1 compression ratio (often, on top of which goes a turbo)
It's all about volumetric efficiency which means stuffing as much as you possibly can, down the hole (the air fuel mix, that is)
I hope this all makes sense and I am sorry I've not yet found any info on the standard octane ratings of British fuel, during WWII.