Doctor Andrew Chesson, of the Rowett Research Institute in Aberdeen, said no technology is risk-free.

He said the currently low level of GM crops grown commercially is set to increase greatly - and thought should now be given to adopting new procedures for safer scrutiny of them.

Doctor Chesson said that when a plant is genetically modified to produce a desired trait, such as insect resistance, it may cause unexpected changes which could lead to new or differing levels of certain chemicals being produced.

'No assumptions'

These may pose a risk to human health, he warned, and new analytical techniques need to be devised to assess that risk.

Dr Chesson said it was of crucial importance that those tests do not rely on current assumptions of what is dangerous.

And of particular concern were GM crops intended for industrial use.

The present method for disposing of crushed and drained oilseed used in the cosmetics industry is to turn it into animal feed.

But he said that if there were hazardous chemicals in the feed a danger exists that they could be introduced into the human food chain.