Britain's official food safety watchdog - which prides itself on its "openness" - is embroiled in a row over the blanking-out of large sections of a document relating to a banned GM maize illegally imported into the country.

The Food Standards Agency had even erased the telephone numbers of the European Commission and the biotech company Syngenta, along with statistics on the total trade in maize between Europe and the US.

The documents, which were finally released under the Freedom of Information Act after weeks of pressure from a small environmental group, GM Free Cymru, help to expose one of the greatest GM scandals of recent years.

As reported in The Independent on Sunday in April, at least a thousand tons of the maize has been illegally exported from the United States to Europe over the past four years.

The Bush administration failed to inform European countries that they were inadvertently importing the maize, which had been confused with a similar approved one. The imports were later exposed by the scientific magazine Nature. Even then it was not revealed that the maize contained a gene conferring resistance to antibiotics that could potentially cause people to resist vital medicines.

The Food Standards Agency refused to try to track down the banned maize in Britain. Having carried out no tests, it says it was "not aware" of the crop's presence. It took action to stop the imports only when forced to do so by the European Commission.

The censoring of the documents is bound to raise new questions about the agency's role in the scandal, and its relationship with giant biotech companies.

Dr Brian John of GM Free Cymru, who has lodged a formal complaint with the agency, said: "After endless procrastination, we have at last been sent a bunch of documents relating to the scandal, only to find that they have been heavily censored in a manner that would have done credit to Stalinist Russia."