It's a 1946 Cisitalia D46 and was entered and driven in the race by Richard Pilkington. It raced in the Voiturette class and Wikipedia says this about the car:
'Using Fiat parts as a base Dante Giacosa designed the D46 which made its successful debut in 1946. Giacosa had a vast knowledge of Fiat bits and pieces as he had designed the legendary 500 Fiat Topolino before WW II. The engine and suspension were directly derived from the small Fiat but extensively modified for racing. The engine received dry sump lubrication and further tweaks considerably increased the power output to 60-70 bhp. With a spaceframe chassis and weighing under 400 kg (880 lb) the available power was more than enough for competitive performance. Dusio's dream of a one model series came to nothing, but instead his D46s started to dominate the voiturette series. Highly talented drivers like Tazio Nuvolari piloted the D46 to multiple successes against more advanced but older racing cars.'
You can read more about the car here.