The Environment Secretary Margaret Beckett gave a qualified go-ahead to the commercial cultivation of genetically modified herbicide-tolerant maize today.

But she told MPs in a Commons statement that the UK should oppose the commerical growing of GM beet and oilseed rape.

Her long-awaited announcement, in the face of widespread opposition from environmental and consumer groups, follows five years of consultations and farm scale trials into the impact of GM crops on the environment.

Mrs Beckett said agreement "in principle" to the commercial growing of GM herbicide-tolerant maize would be "only subject to further important conditions".

She told MPs: "Restrictions should be imposed on the existing EU marketing consent which expires in October 2006 so that this maize can only be grown and managed as in the trials or under such conditions as will not result in adverse effects on the environment."

Mrs Beckett said that in response to concern about the pesticide atrazine that had been raised in the EU, the consent holders should be required to carry out further scientific analysis to monitor changes in herbicide use on conventional maize.

And she said they should submit new evidence if they seek to renew the existing EU marketing consent when it expires in 2006.

Before commercial growing of GM maize can go ahead, separate approval will also be needed under seeds and pesticides legislation for the associated herbicide use.