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The heads of Sane and Mind say Big Brother's mind games may cause long-term problems for contestants.

Marjorie Wallace, the chief executive of Sane, said former housemates Shahbaz and Dawn had both contacted her charity's mental health helpline since leaving the show.

And she accused Big Brother of using mental torture techniques to increase tensions in the house.

Wallace said: "We don't want to be killjoys, but it has become obvious that Big Brother is taking real and serious risks with people's mental health for the sake of entertainment.

"I studied psychology and it's clear that the producers are toying with the contestants using something called experimental neurosis.

"This practice was tested on animals in the 1960s, by providing an irregular and confusing system of rewards and punishments.

"Over time, it was proved to cause serious mental anguish for the animals, and it was eventually banned."

Big Brother chiefs yesterday agreed to meet representatives from Sane. The chief executive of Mind will also attend the meeting, which is set to take place within the next fortnight.

Mind spokeswoman Sophie Corlett said: "The producers have a responsibility to fully support participants during and after their time in the house. Pushing anyone to the edge is bound to have some impact on their mental health."

So far in this series, troubled Glaswegian Shahbaz has quit the house after threatening to kill himself. He has since been treated for depression.

Dawn, who was kicked off the show for alleged rule-breaking, has accused Big Brother of mental cruelty.

She said yesterday: "It's time for this show to finish. They're taking chances with people's wellbeing. I know how Big Brother treats people and it's not right."

A third contestant, posh George Askew, pulled out, saying the pressure of fame was too much for him.

And there have been concerns for the mental wellbeing of recovering anorexic Nikki, cosmetic surgery obsessive Lea, and cross-dressing ex-housemate Sam, of Irvine, Ayrshire.

Wallace said: "Big Brother always says contestants are put through vigorous psychological testing but that's not the case. There are psychologists but they are not always listened to and no one person can ever make a fair judgment on someone's mental capability.

"The kind of people who go on the show are vulnerable by their very nature, and they will have grand ideas of fame and fortune when they leave which often aren't realised."