Found this while search for other subject, source wikipedia
Formula Two
While Formula One has generally been regarded as the pinnacle of open-wheeled auto racing, the high performance nature of the cars and the expense involved in the series has always meant that there has needed to be a path to reach this peak. For much of the history of Formula One, Formula Two represented the penultimate step on this road.
Formula Two was first formally codified in 1948 by FIA as a smaller and cheaper compliment to the big 4.5L Formula One cars of the era. The engines were smaller and less powerful than those used in Formula One, and the cars were also shorter, lighter and cheaper than their big brothers. This encouraged privateer teams such as Cooper to start out in Formula Two, rather than to compete against the big manufacturers of Mercedes-Benz, Alfa Romeo, and Maserati. In fact, Formula One in its early years was so expensive and entrants were so few that in 1952 and 1953 all Grand Prix racing was held using the Formula Two formula!
By the late 1960's however, with the 'Return to Power' of Formula One and the introduction of a new 1600cc engine formula for Formula Two, the junior series assumed its intended role as a feeder series for F1. [[1] (
http://prorallypix.com/cover/ringf2.jpg)] Nevertheless, many Formula One pilots continued to drive the smaller and lighter cars on non-championship weekends, and often Grand Prix grids would be a mix of Formula One and Formula Two cars. Jackie Ickx made his Grand Prix debut in a Formula Two car, qualifying with the fifth fastest time overall! Forced to start behind even the slower Formula One cars, Ickx quickly regained his top position to finish in the points! Less happily, Jim Clark, regarded as one of the greatest race drivers of all time, was killed in a Formula Two race early in 1968, at Hockenheim.
This 'invasion' of Formula One drivers in Formula Two ranks (a situation similar to that of modern-day NASCAR racing) was permitted because of the unique grading system introduced. Any driver with an 'A' grading was not permitted to score championship points. A driver gained an 'A' rating by finishing in the points in two Grand Prix events or the top three in two World Sport Car events. The annual Formula Two champion was also granted an A rating for one year, and a Formula One World Champion was A graded for five. This system permitted young drivers to work towards the championship, while allowing older drivers to keep their hand in during the long breaks between Grand Prix's of the time.
In 1972, the formula was changed to 2.0L, and remained such for the remainder of the series. By the early 1980's however, declining grid sizes and declining interest in the series threatened it with extinction. In 1984, Formula Two disappeared and was replaced with Formula 3000.
List of Champions:
(Except the 1952 and 1953 seasons were Formula Two were used for the World Championship for Drivers, Formula Two never crowned a World Champion, and many nations had their own national series. However, from 1967 a European Championship was conducted in more direct support of Formula One)
1967 - Jacky Ickx - Matra
1968 - Jean-Pierre Beltoise - Matra
1969 - Johnny Servoz-Gavin - Matra
1970 - Clay Regazzoni - Tecno
1971 - Ronnie Peterson
1972 - Mike Hailwood - Surtees
1973 - Jean-Pierre Jarier - March
1974 - Patrick Depailler - March
1975 - Jacques Laffite - Martini
1976 - Jean-Pierre Jabouille - Elf 2
1977 - Rene Arnoux - Martini
1978 - Bruno Giacomelli
1979 - Marc Surer
1980 - Brian Henton
1981 - Geoff Lees
1982 - Corrado Fabi
1983 - Jonathan Palmer
1984 - Mike Thackwell
No Formula Two champion ever won the Formula One Championship.