The poll also named Norfolk-based Lotus as the most popular British manufacturer, with seven of its models making the 100 best British cars list.
Following the Mini at the top of the list was the McLaren F1, with the Jaguar E-type third and the Range Rover fourth.
Jaguar and Ford both had six cars in the top 100, including the Jaguar D-type and the Ford Sierra RS Cosworth, while Aston Martin had five, including the DB5 - a favourite with 007 James Bond.
Created by Sir Alec Issigonis, the Mini achieved worldwide fame, being dubbed the first "classless car". The marque was successfully revived in a larger and more-powerful version by BMW in 2003.
Autocar brand editor Chas Hallett said: "It comes as little surprise that the original Mini has topped the list of all-time British greats.
"It's such an iconic vehicle and represents a lot more than the British car industry; the Mini is associated with Great Britain around the world and, in many ways, it was ahead of its time."
He went on: "Everyone loved and still loves an original Mini. It ensured a fabulous drive every time, with a wheel literally at each corner and a low centre of gravity, plus it was cheap to own and run.
"Many a former owner will undoubtedly be wishing they had held on to theirs, as good examples are now worth tens of thousands of pounds."
This was the Autocar top 10:
1. Original Mini
2. McLaren F1
3. Jaguar E-type
4. Range Rover
5. Yamaha Motiv.E
6. McLaren P1
7. Jaguar XJ220
8. Aston Martin DB5
9. TVR Griffith
10. Ford Escort Mexico