The Austin London Taxicab used a modified Austin Heavy Twelve-Four chassis clothed with new bodies designed by London's largest taxicab retailer and dealer Mann & Overton, and made for them by London coachbuilders.

The Austin Twelve is a motor car introduced by Austin in 1921. It was the second of Herbert Austin's post World War I models and was in many ways a scaled-down version of his Austin Twenty, introduced in 1919. The slower-than-expected sales of the Twenty brought about this divergence from his intended one-model policy. The Twelve was announced at the beginning of November 1921 after Austin's company had been in receivership for six months. The number twelve refers to its fiscal horse power (12.8) rather than its brake horsepower (bhp) which was 20 and later 27. The long-stroke engines encouraged by the tax regime, 72 × 102 mm later 72 × 114.5 mm, had much greater low-speed torque than the bhp rating suggests.