It satisfied our scientific goals

Professor Alex Haslam

The Experiment was an attempt to replicate elements of a 1971 US university study in which students were "imprisoned" to study responses to solitude and oppression by volunteer "guards".

Philip Zombardo, who oversaw the Stanford experiment, said last year that such research was now considered "unethical" and should not be repeated.

Ethical committee

But Professor Alex Halsam from Exeter University denied a Guardian report that the emotional and physical well-being of the 15 BBC participants was in danger of being compromised.

Professor Alex Haslam and fellow psychologist Stephen Reicher from St Andrews were overseeing the BBC experiment, along with an independent ethical committee.

The committee made the decision to halt shooting of the programme after nine days - a day earlier than expected - after consulting with the psychologists.

Professor Haslam told BBC News Online: "It was brought to a conclusion but it was not terminated - it had satisfied our scientific goals.

"In Zimbardo's study it turned very ugly.

"In ours there were a few inter-personal tensions and we didn't want it to escalate, but we'd already got a tremendous amount of scientific data and we didn't need to go any further.

"We had an on-site ethics committee because we didn't want to overstep the line - but in fact we weren't anywhere near the line.

"We did not behave unethically - the participants were all very happy at the end of the study and we were satisfied with our scientific goals," said Professor Haslam.

'No harm'

A BBC spokesman said that the role of the ethical committee and the decision to end the filming showed that the appropriate controls were in place.

"Everyone was very conscious of the previous experiment and the BBC wanted to ensure no harm came to contributors.

"The filming of the programme is done and it will probably be televised in April or May," said the spokesman.