Mr Kennedy was unveiling his party's new policy paper on genetic modification prior to visiting a GM crop test site in Berkshire.

The Liberal Democrats want to widen the public debate on GM foods while introducing stricter guidelines for trial sites in the UK.

Mr Kennedy said: "The government must come clean over GM crops being grown for commercial use.

Charles Kennedy: "The issues have to be addressed properly"

"They must immediately introduce a five year moratorium to ensure sufficient research and testing can take place.

"Only then can we be confident that decisions on future use are properly informed."

The proposals to be debated at the party's upcoming conference include:

• Ensuring genuine public consultation at a local level
• Preventing field trials near to crops which could suffer from cross pollination
• Forcing each proposed site to undergo an independent environmental impact assessment.

The policy paper, Keeping the Balance, also considers other issues such as human cloning and gene patent laws although it concentrates mainly on the GM issue.

Charles Kennedy wants to carve out an environmental agenda

Mr Kennedy said he recognised that GM crops could produce significant benefits but "public confidence was missing at the moment".

He said the government, which announced four new trial sites earlier this week, was "failing and failing badly" on meeting concerns in public opinion.

Mr Kennedy is visiting the Berkshire site with Friends of the Earth activists as well as scientists.

Besieged by activists

Four companies involved in GM crops have told the BBC that nearly half of their trial sites in East Anglia have been destroyed by environmental activists.

The BBC's Robert Pigott: "Several companies have threatened to move trials to France or Denmark"

No one has claimed responsibility for the latest attack on a field of GM sugar beet in Suffolk.

Several companies developing GM crops have warned they may move their research abroad if British trials are not adequately protected from activists.