Salute
Both the Spitfire I and Hurricane I were cleared to use +12 boost with 100 octane fuel on March 20th 1940. By that point, 100 octane fuel was in supply.
There are numerous log entries from RAF Squadrons listing the dates the Squadrons converted as well as many histories mention this and there are many photos of aircraft with the '100' markings, for only 100 octane fuel.
http://www.spitfireperformance.com/no611-100oct.jpg
http://www.spitfireperformance.com/no74-100oct.jpg
http://www.spitfireperformance.com/6...-100octane.jpg
http://www.wwiiaircraftperformance.o...rb-16feb40.jpg
http://www.spitfireperformance.com/603-ross-pg125.jpg
http://www.spitfireperformance.com/r...yce-100oct.jpg
http://www.spitfireperformance.com/price-pg74.jpg
http://www.wwiiaircraftperformance.o.../1940-0897.jpg
http://www.wwiiaircraftperformance.o...er_Station.pdf
http://www.wwiiaircraftperformance.o...banks-fuel.pdf
http://www.wwiiaircraftperformance.o...-42363-319.jpg
http://www.wwiiaircraftperformance.o...cants-pg12.jpg
http://www.spitfireperformance.com/6...ining-film.pdf
http://www.spitfireperformance.com/6...-100octane.jpg
http://www.wwiiaircraftperformance.o...nstry-pg87.jpg
http://www.wwiiaircraftperformance.o...stry-pg191.jpg
http://www.wwiiaircraftperformance.o...r-spitfire.pdf
There were no shortages of 100 octane fuel:
Wood and Dempster wrote in their book "The Narrow Margin":
Quote:
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As it turned out, aviation spirit was to prove no worry for the R.A.F. By July 11th, 1940, the day after the Battle of Britain opened, stocks of 100 octane petrol used in the Merlin engine stood at 343,000 tons. On October 10th, twenty-one days before the battle closed, and after 22,000 tons had been issued, stocks had risen to 424,000 tons. With other grades of aviation spirit total stock available on October 10th, 1940, was 666,000 tons. Oil reserves were 34,000 tons.
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All this information is courtesy of Mike Williams Spitfire site:
http://www.spitfireperformance.com/spit1vrs109e.html
Most of the benefit of 100 octane fuel in the Hurri I and Spit I was at lower altitudes, there was no gain above the rated alt of these planes. Only when the Spit II appeared with a higher boost supercharger at high alt, was there any gain up high.