The Invacar was designed and initially built by Oscar Bertrum 'Bert' Greeves for his disabled cousin, Derry Preston-Cobb in 1948 using a Villiers 147cc engine. Greeves approached the government with the idea of building these for the many war veterans, and they agreed. Contracts to produce the 3-wheelers were awarded by the Ministry of Health to several firms including Harding Ltd, Dingwall & Son, AC Cars Ltd, Barrett, Tippen & Son, Thundersley and Coventry Climax.
In 1972 invalid cars came under attack from the Disabled Drivers Association as being unsafe, and with Stirling Moss as spokesman for the campaign the future for Burt Greeves' Invacar appeared bleak, but it remained in production until 1977. In 2003 the cars were deemed illegal and the vast majority were crushed.
Sources: 3-wheelers.com, et al.