1912 - 1914
This name was used for two distinct types of car whose production was separated by World War I. The first was a close relative of the 13.9hp B.S.A. and although it was sold by the Siddeley-Deasy organisation, it was probably made in the B.S.A. factory. It had a 2014cc 4-cylinder sleeve-valve engine, and was offered with a chassis price of £275 which was £25 more than the B.S.A. Bodies were mostly 4/5 seater tourers. A few chassis for light truck and 14-seater bus bodies were made, using the same engine, and some some were supplied as amubulances to Russia.
The next came in late 1921 when Armstrong-Siddeley formed a separate company to make a light car powered by a 998cc air-cooled V-twin engine with 3-speed gearbox and shaft drive to a bevel rear axle without a differential. The name came from Stoneleigh Park, a large estate near Coventry.
Source: Nick Georgano / The Beaulieu Encyclopaedia of the Automobile