In an experiment, rats were fed potatoes for 100 days which had been modified to make them resistant to pesticides.
After seeing the results of his work at the Rowett Research Institute in Aberdeen, Professor Arpad Puztai said he would not eat genetically modified food.
The findings, he said, raised grave questions about the safety of the food for humans.
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"We are assured that this is absolutely safe and that no conceivable harm could come to us from eating it. But if you gave me the choice now, I wouldn't eat it."
The most worrying feature of the experiment was the effect of the potatoes on the rats' immune systems, he says in ITV's World in Action to be screened in the UK on Monday evening.
"The system is there to fight off all disease-carrying bacteria that get into our bodies.
"If it is damaged and cannot mount a proper response, then we are in trouble."
A growing proportion of processed food available in Britain contains GM ingredients but there are no legal requirements for warning labels on packaging.
MP wants ban
Liberal Democrat environment spokesman Norman Baker, who disclosed last week that GM food had been removed from the menu at the House of Commons, called for a ban.
"The government has been irresponsible and spineless in allowing GM foods into our diet without demanding to see definitive proof that it is safe.
"The only proper thing to do now is to ban GM ingredients from all foodstuffs."
Shadow health spokesman Alan Duncan called for the government to outline its policy on genetically modified food.
He said: "I think that massive forces are being unleashed here.
"The biggest issue is what will be the consequences of putting genetically modified food into the market place and indeed on growing crops?
"Will there be leaching from one field across to another? Will there be long term consequences of which we are not yet aware?''
Government assurances
Foods Minister Jeff Rooker said the government had no immediate plans to call a moratorium on genetically modified foods, but agreed that repeated testing of them would be desirable.
"I think everybody has got to take a precautionary approach on this.
"It isn't a question of it being based on nervousness but being ultra-precautionary when one's tangling with the leading edge of science."
Mr Rooker said the potatoes used in the experiment were not on sale and would not be approved for sale.
"The potatoes have gone wrong because this particular potato damaged the immune system of the animals it was tested on. The fact is, that product wouldn't have got through the regulatory process to be allowed to be marketed as a product."
Growing pressure
Dr Ian Gibson - a member of the Commons Science and Technology Committee and a former Dean of the Biological Science Department of the University of East Anglia - said the pressure for a moratorium would grow over the next week.
"I think the government is going to have to react very quickly and have a top flight meeting to decide on that issue - whether or not there should be a moratorium or not."
Top biotech company Monsanto questioned the fairness of the tests as the rats were fed on an unlicensed crop.
Spokesman Dan Verakis said that they had carried out "intensive safety assessments of new biotech crops" including tests using rats that have had results published in journals.
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