Prime Minister Tony Blair: Before we ban all GM foods, we must proceed on the basis of the evidence

Prime Minister Tony Blair said: "Before we take the step of banning all GM foods why don't we proceed on the basis of the evidence, publish the results of that evidence, and make sure there is proper labelling [in supermarkets]. And then let's have an informed debate, instead of saying, 'well if its GM foods let's ban it all together'".

The calls for a moratorium follow the controversial findings of a British scientist who argues that genetically-modified potatoes have damaged the immune systems of rats.

Cabinet Office Minister Dr Jack Cunningham said Dr Arpad Pusztai's findings "were in dispute" despite the backing given to them by 20 internationally renowned scientists.

Cunnigham: GM foods have "huge" potential

He told BBC News: "We need to clarify what the reality of the scientific outcome of these experiments really is. But it is not a reason to ban all genetically-modified foods."

He added that no GM potatoes were grown or sold in the UK.

Both the Conservatives and the Liberal Democrats favour a halt to the commercial production of genetically-modified foods.

The Shadow Agriculture Minister Tim Yeo said he had written to the prime minister asking him to take immediate action to end the commercial planting of certain GM crops.

Mr Yeo said the government should be making decisions on the basis of clear, scientific evidence.

He claimed Dr Cunninhgam had misled the House of Commons over the position of English Nature, the government's advisory body on conservation, and said the minister should be sacked.

"The government should arrange for the evidence to be assessed by someone more trustworthy than Dr Cunningham to restore public confidence in their handling of this issue," he said.

Cabinet Office Minister Dr Jack Cunningham: We haven't seen any scientific results to justify ban

Liberal Democrat agriculture spokesman Paul Tyler said the scientists were not "scaremongering".

He told BBC News that the scientists who backed Dr Pusztai "are both level headed and suitably cautious".

He said: "I think we need to adopt the same sort of rigorous standards of testing [for GM foods] as we have for pharmaceuticals.

"We are already ingesting tonnes of genetically-modified food over a lifetime. That could have cumulative effects - we simply don't know what they will be.

"Any damage to the immune system of human beings could have calamitous effects in the long run," he said.

Tyler: GM food fears

The Liberal Democrats are also calling for the stricter labelling of GM foods. Many are on supermarket shelves unmarked, although most shops are now stepping up their labelling of GM foods.

A spokeswoman for the Consumers' Association said: "We have asked Tony Blair to conduct a root and branch reform of the regulatory system immediately and until that is done not to allow any new GM food products on to the market."

Dr Cunningham said the government would be "looking at the regulatory system to see if there are any loopholes we need to close."

He added: "The idea that Britain alone can stop these developments is simply not realistic. Biosciences and biotechnology have the potential to bring huge advantages to us in terms of agriculture, health and the environment."