Growing concern that Government-appointed experts have come under pressure from pro-GM peers to toe a bio-tech line has led Tony Blair to appoint Nigel Griffiths, the Minister for small business, to investigate.

Griffiths insisted that the inquiry would avoid being influenced by Government spin. 'I am determined to make sure none of the facts are kept from the public and none of it is spun. I am also making sure that filtered advice from civil servants does not get in the way. This is too much in the public interest,' he said.

The inquiry follows at least two cases in which leading academics selected by the Government told how they were threatened in an attempt to rig a recent official inquiry into GM crops and food.

Dr Andrew Stirling, of Sussex University and a member of the Government's GM science review panel, was warned by a leading member of the scientific establishment his career would be ruined unless he stopped questioning the technology's safety. The pro-GM scientist tried to get Stirling removed from a research project by approaching its funders.

Days earlier, another leading independent academic had told The Observer how he resigned from the science review after fearing his funding might be withdrawn. Professor Carlo Leifert, of the University of Newcastle, also felt it was improper that an employee of GM giant Monsanto had been allowed to draft a key chapter on the safety of GM foods for the science review.

Opponents of GM crops yesterday welcomed any official attempt to investigate whether any other academic or scientist had experienced similar pressure.

Dr Douglas Parr of Greenpeace said: 'We are pleased that the Government seems to be trying to get to the bottom of this. The intimidation of Stirling was a brazen attempt to silence legitimate concerns about GM crops. How many others are holding their tongues on GM issues for fear of losing their funding and academic posts?'

Sue Flook, of the Soil Association - which wrote to Blair demanding an inquiry into the Stirling scandal - said: 'It just shows the power that the companies can have in influencing academics and ultimately the public. It's unacceptable.'

Despite the revelations, Blair's personal scientific adviser, Professor Sir David King, who chaired the GM review panel, has persuaded Stirling not to name his aggressor.

It comes amid growing signs that the Government is cooling its support for GM, publicly at least. Although Blair has backed research into the use of genetic technology in several speeches, last week Ministers said the Prime Minister had in fact never been a 'gung-ho' advocate.

Yet Blair is already bracing himself for fresh criticism over the technology when it unveils its GM crop farm trials next month.

Reports suggest they will show that GM crops can be more damaging to neighbouring fauna than conventional strains of sugar beet, maize and oilseed rape.

Three varieties of GM crops have been tested in hundreds of farm-scale trials. The Government is to base its decision on whether to grow GM crops commercially in Britain on the results of these trials.