http://en.wikipedia.org/wiki/Peel_P50

The Peel P50 was a three-wheeled microcar manufactured in 1963 and 1964 by the Manx Peel Engineering Company, retailing for £199 when new.[1] It was designed as a town car and was advertised as capable of seating "one adult and a shopping bag."
The makers claimed it was capable of an impressive 100 UK MPG (2.8L/100km, 83 US MPG).[1] Despite its diminutive stature, the Peel P50 is street-legal in the UK.