A number of supermarkets are following the advice of the Food Standards Agency (FSA) and leaving suspect GM rice on their shelves. Others, however, have said they are withdrawing the rice due to consumer concerns.

The FSA's stance has been strongly criticised by a former GM adviser to the US government's Food and Drug Administration, Doug Gurian-Sherman. "We should be taking a more cautious approach," he told the Sunday Herald. "Risks should not be taken with public health for the convenience of companies or of government. It sets a very bad precedent to make safety assessments based on data that is incomplete."

According to Gurian-Sherman, now with the Centre for Food Safety in Washington DC, there simply was not enough evidence to judge whether the contaminated rice was safe or not. "I wouldn't eat it myself," he said.

The Bush administration told European governments last month that US long grain rice had been contaminated by a GM strain known as LL601. The cause is still under investigation, but the gene is thought to have leaked from field trials of GM rice in the southern states more than five years ago.

Last week, the European Union reported that traces of LL601 had been found in 33 out of 162 samples tested by the European rice industry. Contaminated rice has been detected in Germany, France, Sweden, Switzerland and The Netherlands.

In the UK, however, the FSA is not expecting test results for two weeks. But the agency accepted that rice on sale in the UK is likely to be contaminated with LL601, as did the rice industry.

"US long grain rice containing low levels of GM could already have been imported into the UK, including Scotland," said an FSA spokeswoman. "The presence of the GM rice is illegal at any level."

But the FSA insisted that the rice was safe to eat. "Given the very low levels of GM rice, we suggested to the industry that we didn't expect them to withdraw products on food safety grounds," she added.

The FSA is, however, working with the rice industry to prevent any more contaminated rice from entering the country. "The material will undoubtedly be in the food chain, though at very low levels," said Alex Waugh of the Rice Association, which represents UK rice millers.

The UK's biggest supermarket chain, Tesco, said on Friday that it had withdrawn Tesco American long grain rice in 500g and one-kilo bags as a precaution "pending further investigations".

Though Sainsbury's had stopped buying American long grain rice, it was still contained in products on sale. "If any of our customers are uncomfortable eating the rice, they can take it back to their nearest Sainsbury's store where a full refund will be offered," said a spokeswoman for the company.

Waitrose said only that it was "following FSA advice on this issue". The Co-op said its suppliers had confirmed that none of the supermarket's long grain rice products were "implicated". The FSA's stance has been condemned by environmental groups, who are calling for suspect stocks of US rice to be withdrawn.

"It is outrageous, and quite probably illegal, that the FSA is doing nothing to protect consumers from this unauthorised GM rice," said Anthony Jackson of anti-GM campaign group, the Munlochy GM Vigil.

"The FSA has known about this for nearly a month, the US authorities since January, and imports may have been arriving for the last few years. The cover-up attempt must stop now."

The Green MSP Mark Ruskell said: "I cannot understand how it can be deemed acceptable to just leave contaminated illegal products on the shelves."

He voiced concerns that the Scottish Executive was about to introduce a "coexistence" regime allowing GM crops to be grown alongside conventional and organic crops. This would "let the GM genie out of the bottle," Ruskell warned.