That use of carburetors meant the Spitfire and Hurricane couldn't fly inverted for more than about 10 seconds of level flight before the engine would cut out, whereas Me109 pilots were able to, and did, adopt inverted flight in attacks on B17 bombers. This meant they were able to use the underside of their plane as something of a shield against the B17's guns, instead of their cockpit being in full view of the gunners. Apparently around 10% of fighter pilots were on leave during the Battle of Britain. On phoning their bases to ask if they were required, they were told to stay where they were. Could have been because there weren't enough aircraft for them, but it's something that was hushed up.