Educational Testing Service (ETS) Europe is being paid £165 million of public money over five years to mark key stage tests for schools.

This is its first year in the role and it has already run into problems, prompting complaints from head teachers, MPs and the exams regulator over delays in returning test results. Other apparent problems have involved its software, helpline and face-to-face training.

It took over the marking of 9.5 million papers from the exam board Edexcel. ETS Europe is part of ETS, a huge non-profit making American organisation with extensive test administration experience in 180 countries.

In the US it is responsible for running SATs tests, but recently lost the contract for the Graduate Management Admission Test, worth a reported £100 million. It has a controversial history of alleged mistakes in its marking of American test papers. These included inaccurate scoring in an exam used to license teachers in 2004, resulting in more than 4,000 people failing when they should have been given a pass.

In 2006 ETS announced a year-long delay in introducing revised exams for graduates. A spokeswoman for the Princeton Review, an education company, said at the time: “ETS has never met a deadline they have set. We are not surprised at all.”

An ETS spokesman said recently that he had no knowledge of any previous problems in other countries. However, that ETS was given an important contract was heavily criticised. Nick Gibb, the Tory schools spokesman, said: “There was a clear lack of due diligence taken when awarding this contract.”

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