[winny]

As I said earlier in the thread.. All operational Hurricane, Spitfire and Defiant Squadrons in the RAF had been converted to 100 Octane by May 1940

Taken from Spitfireperformance.com

The use of 100 octane fuel was approved for Spitfire Squadrons by 24 September 1938. Fighter Command noted on 6 December 1938 that Duxford, Debden, Northholt and Digby had received 100 octane fuel. As of December 1938 Nos. 19 and 66 were based at Duxford and were the only RAF units then equipped with Spitfires.

The Air Ministry noted in a memo dated 12 December 1939 that "100 octane fuel is approved for use in Hurricane, Spitfire and Defiant aircraft, and state that issue will be made as soon as the fuel is available in bulk at the distribution depots serving the Fighter Stations concerned." Gavin Bailey concluded that "The actual authorisation to change over to 100-octane came at the end of February 1940 and was made on the basis of the existing reserve and the estimated continuing rate of importation in the rest of the year." As of 31 March 1940 220,000 tons of 100 octane fuel was held in stock.
The Co-ordination of Oil Policy Committee noted in the conclusions of their 18 May 1940 meeting with regard to the "Supply of 100 Octane fuel to Blenheim and Fighter Squadrons" that Spitfire and Hurricane units "had now been stocked with the necessary 100 octane fuel". The Committee recorded that actual consumption of 100 octane for the 2nd Quarter 1940 was 18,100 tons.

Wood and Dempster wrote in their book "The Narrow Margin":

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.

Wood & Dempster’s "The narrow margin" shows figures for stocks of 100 octane are in agreement with those of the War Cabinet, however, their figure of 22,000 tons issued falls short of the Air Ministry’s figures as shown below.

By 7 August 1940 "authority has been obtained for the use of 100 octane fuel in all operational aircraft and that instructions to that effect are being issued to Commands",

i.e. all operational aircraft in Bomber, Coastal, Training and Fighter Commands.
On October 29, just before the end of the Battle of Britain, 423,400 tons of 100 octane fuel was in stock in the UK. The War Cabinet recorded that 100 octane stocks stood at 202,000 tons on 31 December 1939 and that 100 octane stocks had risen to 499,000 tons one year later on 31 December 1940. The Air Ministry recorded that 58,000 tons of 100 octane were issued during the Battle of Britain. The War Cabinet recorded that 100 octane consumption within the UK for the whole of 1940 amounted to 130,000 tons, an average of 2,500 tons per week. Consumption of 100 octane during the Battle of Britain averaged 10,000 tons per month for the months of July and August rising to 14,000 tons in September followed by 17,000 tons during October. Total consumption of 100 octane fuel during the Battle of Britain therefore was on the order of 50,000 tons.