Study was based on manipulation, say protesters. Zoe Corbyn reports.

About 40 academics from both sides of the Atlantic have called for the withdrawal of a research paper that purports to show that consumers prefer genetically modified corn.

In a letter to the editor and the editorial board of the British Food Journal, academics including biologists and scientific ethicists claim that the journal failed to act on evidence showing that the research was based on unreported manipulations of shoppers' preferences.

The 2003 paper, 'Agronomic and consumer considerations for Bt (a type of soil bacterium) and conventional sweetcorn', by Douglas Powell at the University of Guelph, Canada, and others, reports the results of a study carried out at a Canadian farm store.

The study found that sales of GM corn were 50 per cent higher than those of non-GM corn.

Controversy erupted in 2006 after the publication of a photograph of a sign displayed in the store during the experiment. Hung above the non-GM corn and listing pesticides used in its production, the sign read: 'Would you eat wormy sweetcorn?' A sign over the GM corn called it 'quality sweetcorn'.

The journal responded at the time by publishing a letter containing the criticism, along with a reply from Professor Powell that conceded that the 'wormy corn' sign had been present on the day the experiment began but said it was 'changed' a week later.

But signatories to the letter say evidence has emerged that suggests the sign was present during a more 'substantial part' of the experiment.

The signatories, led by Joe Cummins, an emeritus professor of genetics at the University of Western Ontario, say the evidence comes from a computer scientist who analysed a photograph provided by one of the study's authors.

Enlarging and realigning the image shows a sign in the photograph - difficult to read with the naked eye - that appears to be the same 'wormy corn' sign.

'The controversy is over whether the sign was changed the following week, and it (now) seems it was not,' said Richard Jennings, a lecturer in ethics in science at the University of Cambridge and a signatory of the letter. 'Until (the paper) is retracted, you have faulty conclusions in the scientific record.'

The paper's lead author, Professor Powell, said: 'I'm not sure there is any new evidence ... Dissent and disagreement in science is normal.

'I personally welcome constructive criticism of my work as a way to continually improve. The research conducted in 2000 was an attempt to gauge consumer preferences. The most difficult task we faced was ensuring that GM and conventional sweetcorn and potatoes remained segregated and tracked from field to retail so sales could be accurately documented.'

Chris Griffith, editor of the BFJ, said he had seen the letter and had replied, reiterating that the journal had published an exchange of letters and that the original paper had been subject to double-blind peer review.

'If anyone is still unhappy then perhaps they should undertake their own research to prove or disprove the original findings,' he said, adding that he was acting on advice from the Council of Scientific Editors.

The decision not to retract the article was 'in the interest of a healthy scientific debate', said a spokesman for Emerald, the publisher of the journal.

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