Mr de Gruchy, General Secretary of the National Association of Schoolmasters and Union of Women Teachers, said he had evidence from teaching unions in the United States that casts doubt on the effectiveness of the Edison Project's privatised schools.

He told BBC News Online that he wanted the government to examine the information closely before "entering into a dodgy deal".

The company claims the evidence compiled against it is selective and biased.

The American Federation of Teachers says there are other schemes more worthy of attention

The Edison Project, a company that runs 25 state schools for profit in the US, has already had meetings with officials from the Department for Education and Employment to discuss a possible involvement in action zones in England. It says further discussions are planned for the near future.

The department will not yet comment on who is involved in the 60 bids that have been made to run the zones, on the grounds of commercial confidentiality, but has not denied that Edison might be among the bidders.

The American Federation of Teachers, which represents almost a million school staff, has research showing that Edison Project schools have a tendency towards high class sizes, a reliance on inexperienced teachers, high staff turnover and a cutting of administrative support.

The apparent success of the Edison Project, says the research, can be attributed to factors such as longer school days, motivated parents and the use of a reading programme which is not specific to the company's schools.

Even with these advantages, the report says that there is no clear improvement in pupils' levels of achievement. It says a failure properly to implement the reading programme is jeopardizing its well-established effectiveness elsewhere.

And Mr de Gruchy points to the Federation's conclusion that "Edison's reports and promotional materials often overstate their schools' success and actual results are, at best, modest".

Edison: union claims 'distorted'

The Edison Project, led by former Yale University president and entrepreneur Benno Schmidt, has gained a reputation in the United States for making improvements in failing, inner-city schools, while also making sufficient savings in running costs to create a profit margin for the company.

Pupils attend the school without charge, while the local authorities pay the Edison Project a management fee for taking charge of the school.

Rejecting the Federation's claims as "distorted" and "partisan", the Edison Project says that in its schools "achievement is generally and clearly on the rise", as witness the waiting lists of families trying to get their children in.

The company also disputes the claim of high class sizes, saying that its classes reflect the local average.

"By any objective standard", says the Project's response to its critics, "the overwhelming majority of Edison schools are off to promising starts, as measured by student achievement, parent satisfaction and other critical indicators of school performance".

Assisting the Edison Project's bid to play a part in the action zones in England is James Tooley, research fellow at Manchester University and director of education and training at the right-wing think tank, the Institute of Economic Affairs.

Mr Tooley believes the company has much to offer, with funds for investment, a readiness to experiment and a programme that involves putting information technology into the homes of students.

In support of the involvement of private enterprise in British schools, he also makes the point that if a company such as Edison fails to deliver what it promises, education authorities can end the experiment and look for services elsewhere.