Flying a Spitfire inverted

In episode 5 we see Flash flying his Spitfire upside-down. It is a well known fact that the standard carburettor in the Merlin engine would not allow this. At least certainly not in 1940...

The early versions of the Rolls-Royce Merlin engine came equipped with a SU carburettor. When these aeroplanes performed a negative G force manoeuvre (pitching the nose hard down), fuel was forced upwards to the top of the float chamber of the carburettor rather than into the engine, leading to loss of power. If the negative G continued, the fuel would collect in the top of the float chamber, forcing the float to the floor of the chamber. This would in turn open the needle valve to maximum, flooding the carburettor with fuel and drowning the supercharger with an over-rich mixture. This would lead to a rich mixture cut-out, which would shut down the engine completely

Complaints from the pilots led to a search for a solution. Beatrice 'Tilly' Shilling, a young female engineer working at the Royal Aircraft Establishment at Farnborough, came up with a solution. She introduced a simple flow restrictor: a small metal disc much like a plain metal washer. The restrictor orifice was made to accommodate just the fuel needed for maximum engine power, the power setting usually used during dogfights.

While not completely solving the problem, the restrictor, along with modifications to the needle valve, permitted pilots to perform quick negative G manoeuvres without loss of engine power. This improvement removed the annoying drawback the RAF's Rolls-Royce Merlin-powered fighters had had in comparison to the German Messerschmitt Bf 109E machine, whose Daimler-Benz DB 601 inverted V12 powerplant had possessed fuel injection since 1937. Miss Shilling travelled with a small team around the countryside to one RAF base after another in early 1941 fitting the restrictors, giving priority to front-line units. By March 1941 the device had been installed throughout RAF Fighter Command. Officially named the 'R.A.E. restrictor', the device was immensely popular with pilots, who affectionately named it 'Miss Shilling's orifice' or simply the 'Tilly orifice'.

(source: https://en.wikipedia.org/wiki/Miss_Shilling%27s_orifice )