US officials did not authorise use of a chemical mixture that killed a British government scientist in an explosives accident, an inquest has heard.
Terry Jupp, 46, suffered massive burns on a testing range at Shoeburyness, Essex, in August 2002.
He was part of a British-American team investigating homemade bombs that could be used in terrorism.
The inquest was also told of American concern that the British were not sticking to planned experiments.
The inquest heard that the American official who commissioned the research had not given permission for Mr Jupp's experiment.
Mr Jupp died after a 10kg mixture of three undisclosed substances caught alight. He died from his injuries six days later.
The test had been planned by a joint US-UK team of scientists, after being commissioned by an official referred to as "Person A" from Washington's National Security Council.
Person A has refused to give evidence in person to the inquest, but his statement was read out to the jury.
In the statement, he said that the precise nature of the test had to remain secret because it would be catastrophic if the results got into the wrong hands.
But he said that he had not authorised the mixture of the substances that spontaneously combusted.
"Person B", another US official who refused to attend, made a witness statement which was read to the jury, in which he described working with Mr Jupp on the day of the accident.
He said that during the preparations, the Americans became concerned that the British scientists were considering experiments that had not been part of the day's plan, including using dangerous chlorates.
The official said: "I heard 'Person E' [a third American official] say, 'if you are going to mix chlorates, I'm going to get Person B and we are going to the next county to listen to you mix it.
"In my opinion, I believe that E stopped a potential accident from happening by not mixing chlorates."
The team decided to press ahead with other tests and shortly after lunchtime, Mr Jupp made final preparations for a firing.
Person B heard a loud noise and felt great heat from a fireball. Mr Jupp fell to the floor and Person B rushed to hose him down with water, the inquest heard.
Mr Jupp worked for the Defence, Scientific and Technology Laboratory.
His family believe that the secret national security experiments were conducted without the Ministry of Defence taking adequate precautions against the possibility of an accident.
The inquest at Southend-on-Sea continues.