The scientist whose experiments on rats sparked the storm over genetically-modified (GM) plants is to tell a parliamentary committee why he is concerned.

The BBC's Pallab Ghosh: "The research created a scientific and political storm"

Dr Arpad Pusztai will give evidence on Monday afternoon with his former colleague at Aberdeen's Rowett Research Institute (RRI), Professor Philip James, to the House of Commons Science and Technology Committee.

It is considering how the government assesses the possible risks of GM foods, and their effect on human health and the environment.

In a television interview last August, Dr Pusztai described how he had fed rats with GM potatoes.

Effects detected

Science Reporter Pallab Ghosh: Dr Pusztai is enthusiastic about GM technology

The potatoes had been engineered to produce a lectin, a protein from a snowdrop.

He said the animals used in one experiment had shown slight growth retardation, an effect on the immune system and changes in the weight of their internal organs.

Dr Pusztai felt there was "'room for concern"

The institute suspended Dr Pusztai, and then refused to renew his contract. But the furore was reignited in February when 20 international scientists signed a statement supporting him.

Meanwhile, an audit committee set up by Professor James concluded that Dr Pusztai's data did not support his conclusions.

Many scientists believed the experiments were interesting but irrelevant, for two main reasons:

• Lectins are likely to produce the sort of effects seen in the experimental rats in any case, whether or not they have been genetically transferred.

• And the GM potatoes Dr Pusztai used were not intended to be used as either human or animal feed, nor was there any plan to use any food containing lectins.

In lay terms, they argued, what Dr Pusztai had done amounted to proving that poisonous potatoes are likely to poison you.

None of that alters the fact that there are real concerns about GM crops.

Some concerns centre on their possible effects on health, some on their potential for harming wildlife and for escaping into the environment.

Lives shortened

The Scottish Crop Research Institute has published research that found adverse effects in ladybirds when they were fed on aphids which had fed on GM potatoes.

It found the female insects' lifespans were halved and their reproduction reduced.

The experiments used potatoes similar to some of those used by Dr Pusztai, modified to include snowdrop lectin.

New study suggests ladybirds are at risk

But New Scientist magazine says several experts regard Dr Pusztai's data as "impossible to interpret".

One of them is Paul Brantram. of BIBRA International, which specialises in toxicity testing.

Even if Dr Pusztai's data are statistically significant, he says, they establish nothing, because in every experiment but one the rats became malnourished.

"Organ weights fluctuate up and down unpredictably in such stressed animals.

"You would expect spurious statistically significant differences just due to biological variation in the response to starvation."

In one experiment, D249, Dr Pusztai fed the rats on raw potatoes. His critics say that experiment is meaningless, because all raw potatoes are toxic.

Dr Pusztai himself accepts that the subject has been blown out of all proportion by the media.

But he says: "On the basis of what we saw, we felt there was room for concern."