The panel of six judges said he must stand trial on two charges - one for cultivating cannabis and the other for possession.

Controversial role: Harrelson in The People vs Larry Flynt

Harrelson planted the seeds in June 1996, knowing he would be arrested, so he could challenge a Kentucky law outlawing possession of any part of the cannabis plant.

He is also campaigning for Kentucky farmers to be allowed to grow hemp legally.

In the past Harrelson has said hemp was Kentucky's leading cash crop 50 years ago and could be again, particularly for farmers wanting to abandon tobacco.

The actor also owns a California firm, Hempstead Co, which sells textiles made from hemp - also used in shampoos, paper and other products.

The company currently has to import raw hemp from China and Hungary.

Marijuana was outlawed in the US in 1937, although hemp was widely grown during World War II to make rope and other materials.

A vegan environmentalist, Harrelson was arrested, along with eight other activists, for climbing the cables on San Francisco's Golden Gate Bridge two years ago. They were demanding government protection for northern California's redwood forests.