The head of the American Association of Professors has accused BP of trying to "buy" the best scientists and academics to help its defence against litigation after the Gulf of Mexico oil spill. "This is really one huge corporation trying to buy faculty silence in a comprehensive way," said Cary Nelson.

BP faces more than 300 lawsuits so far. In a statement, BP says it has hired more than a dozen national and local scientists "with expertise in the resources of the Gulf of Mexico".

The BBC has obtained a copy of a contract offered to scientists by BP. It says that scientists cannot publish the research they do for BP or speak about the data for at least three years, or until the government gives the final approval to the company's restoration plan for the whole of the Gulf.

It also states scientists may perform research for other agencies as long as it does not conflict with the work they are doing for BP. And it adds that scientists must take instructions from lawyers offering the contracts and other in-house counsel at BP.

Bob Shipp, the head of marine sciences at the University of South Alabama, was one of the scientists approached by BP's lawyers.

They didn't just want him, they wanted his whole department.

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