THE organisers of Comic Relief can laugh all the way to the bank with the charity proceeds of Celebrity Big Brother, but the housemates have had the smiles knocked off their faces. They've discovered the hard way that sitting in a bath of cold baked beans, shaving your head or simply writing out a cheque are a lot less painful ways of contributing to Red Nose Day.

Fifteen minutes of fame may be bearable, but a whole week of being imprisoned and your every move observed by cameras - and consequently millions of TV viewers - is like being strapped into the psychiatrist's chair.

What began as a game for a laugh turned deadly serious as Vanessa Feltz lost her cool, Anthea Turner got tearful and Jack Dee went stir crazy. Suddenly saying: "But it's for charity", seemed like a lame reason for exposing themselves so publicly.

Why, we ordinary mortals want to know, would six relatively-famous people - or "a bunch of desperate celebrities trying to revive dwindling careers", as original Big Brother housemate Nasty Nick called them - subject themselves to such an ordeal? Surely they're not stupid, although anyone photographed with a chocolate bar in their wedding photos has already shown poor judgement in most people's eyes.

But still it seems as if Turner and her fellow housemates reckoned without the massive public interest Celebrity Big Brother would generate. After her eviction, the ex-Blue Peter presenter's spokesman admitted: "I don't think she ever realised just what level of interest this whole thing would produce."

Considering Channel 4's original Big Brother was the TV phenomenon of last year and was accompanied by endless media coverage, this seems a very naive attitude.

"You really have to admire these people for doing it. They really are putting themselves on the line. There are other things they could do for charity. They are probably assuming they will come off well," says Dr Sandy Wolfson, principal lecturer in psychology at the University of Northumbria.

"They are putting themselves in a potentially-embarrassing position, risking rejection and saying something they might regret. Nobody likes rejection, even ordinary people, but particularly people in the public eye. It's not something people enjoy."

Doing something for charity is perhaps only part of their motivation. Dr Wolfson says: "People in public life might have already accomplished quite a bit but are continually challenging themselves to achieve other things. So it's probably quite a positive thing for them to do. It seems it might be quite good fun."

"In the first Big Brother series people stood to gain something financially as well as the publicity. Maybe these celebrities have the self-esteem to believe they can't do anything wrong. You would have to have a relatively secure view of yourself and probably be a high risk-taker, knowing all kinds of things can happen and you'd have to deal with them."

Certainly Turner, whose golden girl reputation has become tarnished through publicity about her private life, and Feltz, who has suffered a humiliating marriage break-up in the past year, may have hoped to regain public popularity by showing themselves as good sports in aid of charity. Clearly, neither had reckoned on the psychological effect of being incarcerated and forced to live by a set of strict house rules.

Turner looked close to tears when she was one of the first to be nominated by fellow housemates for eviction. Now, she may just have been going for the sympathy vote and be a very good actress, although someone I know who saw her in pantomime in her early post-Blue Peter days thought that unlikely. She seemed genuinely hurt that the public really didn't like her.

Dr Wolfson says: "You could see that reaction of the two people nominated was very different. I don't think Chris Eubank had any major problems but you could see Anthea Turner was very upset. Given that these people's livelihoods depend on not being rejected, it probably is quite disturbing at some point.

"Of course, it could be a way of redeeming yourself and showing a side of yourself that the public don't see to improve your image."

After the public voted out Eubank rather than Turner, she perked up no end - thankful, no doubt, for proof that she wasn't the most unpopular person in the country.

It all became too much for Feltz, who went on a drastic diet and image makeover after her marriage broke up, when she was nominated. She told Big Brother to eff off and was seen scrawling words on a blackboard. Not a pretty sight, but not as bad as the sight of her taking off her knickers as she got undressed for bed.

Post-eviction, Feltz went on a damage limitation campaign, giving endless interviews to assure everyone she was perfectly all right, felt proud to have defied Big Brother and, after all, it was only a game for charity. Those who'd seen her emotional turmoil inside the house may have found that difficult to believe.

Whether the experience will leave the housemates scarred for life is debatable. "You would hope there's no lasting damage," says Dr Wolfson, "but there's always the possibility they will do something that would upset the others in the group. Hopefully people are doing it in the spirit in which it's intended - for charity. You could say that for certain people any publicity is good publicity."

The problem is that, with the exception of Brookside actress Claire Sweeney, the celebrities are famous for being themselves, not playing a role. There's nowhere for them to hide in the Big Brother house and no script to read from the auto-cue. They're on their own without even a make-up artist or hairdresser.

Being natural comes hard when celebrities take increasing control of their public image. There's no press officer to ward off questions and no contract with a glossy magazine to ensure only the pictures you want published appear.

For people in a profession which constantly complains about public and press intrusion, it was not the wisest move to lay themselves open to such uncontrolled scrutiny. Viewers are only seeing 30 minutes or so footage a day - and you can't blame the editor for selecting the juiciest bits - but the chance to watch people you know from the telly or sport having to live "ordinary" lives is one that couldn't fail to capture the nation's imagination.

Millions became caught up in the antics of the original Big Brother housemates who were neither famous nor particularly interesting. One of the downsides of the programme is that it has brought Nasty Nick out of the woodwork to commentate on the celebrities' behaviour.

One problem facing the celebrities is that the public are taking it too seriously and reading more into their behaviour than intended. Dr Wolfson says: "For us, there is an element of voyeurism about it. When you watch these kinds of show, it's almost a way of increasing your own self-esteem because you see famous people and, if they can get rejected and put themselves in embarrassing position, then things are not so bad for us."

One of the early favourites to win was Claire Sweeney, which isn't perhaps surprising as she doesn't have a public image to live up to. At least, we can be thankful she isn't behaving like her Brookside character Lindsay Corkhill - a gun-toting gangster and occasional lesbian.

Comedian Jack Dee has been so keen to live up to his miserable image that viewers may well grant his wish to expel him, although we shouldn't underestimate the following of Boyzone which could well benefit singer Keith Duffy.

The real winner, of course, will be Comic Relief with over £300,000 raised so far - part of the cost of a telephone vote goes to the charity.

* The winner of Celebrity Big Brother will be announced tonight after 10.35pm during Big Red Nose Night on BBC1. An omnibus edition of Celebrity Big Brother is being shown on Channel 4 at 9.15pm tomorrow.

Read more about Comic Relief at our red nose website.