The GM crops row escalated yesterday after reports that a major experiment will prove they are worse for the environment than normal crops.
The results will be a blow to the Government - believed to want to increase the range of GM foods sold in shops.
But scientists are now expected to now advise them to be banned in the UK.
A three-year trial of three crops was set up after fears declining farmland species might be further damaged by GM crops. Conventional crops were grown in adjacent fields.
The results, published next Friday, are said to show that two of the strains - GM oil-seed rape and GM sugar beet - damage plant and insect life.
The third, GM maize, allows survival of more weeds and insects but some scientists still have reservations. In a recent survey 93 per cent of shoppers wanted GM foods banned.