Three students have complained after their university study trip to North Korea was used as cover for a BBC documentary on the communist state.

Professor George Gaskell, pro-director at the London School of Economics, said the university authorities were unaware until last week that the BBC had used a ten-person party as cover for an eight-day trip by Panorama to the country.

The professor said, had veteran journalist John Sweeney been caught, the party - which included an 18-year-old student - could have found themselves held in solitary confinement in a North Korean prison.

Today, the BBC's head of programmes Ceri Thomas indicated the students had been paid for their co-operation when he said "no money changed hands" until the corporation had talked to them twice before they left London.

He also admitted the students were not told about a two-man film crew on the trip until they arrived in Beijing, en route to Pyongyang.

The LSE is calling for the BBC to pull the documentary, which is due to be broadcast tomorrow night.

Professor Gaskell said it could jeopardise the work of its academics who are working in sensitive countries around the world, including China.

The BBC has already agreed to pixelate the images of the three students who have complained.

Speaking on BBC Radio 4's The World this Weekend, Professor Gaskell said: "We were told the BBC had undertaken a risk assessment and that it had been approved at the highest level.

"Now LSE believes that any reasonable assessor of risk, or indeed any parent contemplating their son or daughter going on such a trip with the involvement of the BBC, would have thought the risks quite unacceptable.

"The chairman of our council, Peter Sutherland, wrote to Lord Patten (chairman of BBC Trust) and said that in view of this deception the LSE received an unqualified apology from the BBC.

"I think there is less danger to students than there is to my colleagues. Some of my colleagues at the present are in Africa, China and various other sensitive countries.

"If there independence and integrity is challenged, they may find themselves in considerable risk."

He added: "We clearly have a different opinion about what is an acceptable risk. I think the situation in which the students found themselves was potentially extremely dangerous.

"Had we been sitting around hearing about this trip for the first time, I think it was Monday or Tuesday, wondering about how we were going to get these students out of solitary confinement in some North Korean jail, I think the students' view on whether it was such a good idea might have been quite different."

But Mr Thomas defended the action and said the documentary was a "very, very important piece of public interest journalism", telling the same programme the access the trip provided - which would not have been given to a journalist - justified putting the lives of the students at risk.

He said: "We have a duty to give enough information to people on a trip like this so that they can give us fully informed consent. There were ten students. We talked to them twice before they left London, before any money changed hands.

"We told them there would be a journalist on the trip and that if that journalist was discovered it could mean detention, that it could mean arrest.

"They were consenting to the risks that were implicit of having a journalist on that trip. We had a further conversation with the group when they arrived in Beijing en route to Pyongyang and at that point we told them that it was John Sweeney and that it was a film crew and so before they entered the country again they had full knowledge of what was being done as well as the core fact, the material fact, is that they were made fully aware of the risks and the implications of those risks were the journalists to be discovered."

He added: "These were not teenagers just out of school. The youngest was 18 and we know for a fact that he or she specifically consulted his or her parents before agreeing to go on the trip.

"The other nine were between 21 and 28 and were experienced in making decisions for themselves.

"Three of them have asked since the trip returned that their images be taken out before the documentary goes out tomorrow night and we have consented to that. They will be pixelated or blobbed in the film so you won't be able to identify them.

"I would say that the only people we deceived in the making of this film was the North Korean government and we did that because we thought it was a necessary condition to get in to this country which is hidden from view and is absolutely essential to world events at the moment."

Mr Sweeney had used the study trip so that he could secretly film inside the communist state, which has in recent weeks made repeated threats to attack the United States, South Korea and their allies.

He defended the BBC's decision to use the trip to gain access to North Korea.

Speaking on BBC News, Mr Sweeney said: "All of the students on the trip are grown-ups. They are big people and I know them - they are brave and good. All of them were told twice that a journalist was coming. I was that journalist and I used my own name. I am also as it happens an LSE graduate.

"I told a lie. It was difficult. However, we are getting in to a state which is frankly more like Hitler's Germany than any other state in this world right now. It is extraordinarily scary, dark and evil. All of the students on that trip, could have if you like, dobbed me in. None of them did. The majority of students support this programme."

But Tory MP Rob Wilson said he was concerned by the decision to use the university trip as a cover.

He said: "If I were a parent of the young people involved in this trip to North Korea I would be very concerned that the BBC could be so reckless with the safety of my son or daughter.

"We know how unstable North Korea is and how little the country cares about the views of the international community, so this could have ended in tears.

"The fact that it did not still leaves open the question as to whether the BBC should be paying young people to put themselves at risk and, as it transpires, probably without all the salient facts about the dangers.

"There must also be a concern that North Korea will act against future student and university trips in a heavy handed manner. None of us can be entirely sure how the country will react.

"I do understand that brave journalism, and you do need to be brave to go to North Korea, does take risks but it's not usually with the lives of other young people. I also know that getting inside and properly understanding North Korea is highly desirable.

"I guess the question for the BBC is can it justify this as a morally acceptable piece of journalism? We should all listen carefully to the answer given by the BBC."

Alex Peters-Day, general secretary of the LSE Students' Union, accused the BBC of using the students as "human shields". She said it had put at risk future trips by LSE students, telling the BBC News channel Mr Sweeney's actions were "reckless".

Ms Peters-Day said: "The only thing to come out of this is that I am so grateful that we are not in a situation where we are seeing how we have to remove our students away from a detention camp in North Korea.

"I think the trip was organised by the BBC as potentially a ruse for them to get into North Korea and that's disgraceful.

"They've used students essentially as a human shield in this situation."

Earlier, the LSE's director, Professor Craig Calhoun, accused the corporation of "lies and deception from the outset" and of putting the students at risk, telling Sky News it was "unwilling to take responsibility" for the risks it has caused.

But the BBC denied giving students insufficient information about the plans for secret reporting.

In a statement, a Panorama spokeswoman said: "We recognised that because it could increase the risks of the trip, the students should be told in advance that a journalist intended to travel with them, in order to enable the students to make their decision about whether they wanted to proceed.

"They were given this information, and were reminded of it again, in time to have been able to change their plans if they wanted to.

"The students were all explicitly warned about the potential risks of travelling to North Korea with the journalist as part of their group.

"This included a warning about the risk of arrest and detention and that they might not be allowed to return to North Korea in the future."