And when did you first see your father?

A SHEEPISH-LOOKING young man walks into a small, windowless room, clutching a magazine. Ten minutes later he re-emerges, face a little flushed, a small bottle in his hand and £15 richer.

Fast forward 18 years. Now approaching middle age, he is settling down on the settee with his wife for a night in front of the television, with his young children safely tucked in bed upstairs. Then comes a knock on the door and, as he opens it, he is greeted by a strange, yet vaguely familiar, face. "Hello dad," the visitor says.

Little did he realise that his youthful act of charity - or quick way of earning beer money - would result in the figure before him. Or that his offspring would one day come to find him.

But that is now becoming a real possibility. The Government is looking at ending the anonymity of sperm - and egg - donors which has been in force ever since artificial insemination was introduced in this country. And yesterday, Baroness Warnock, one of the most influential voices in the field, said she was in favour of the move.

As chairman of the Committee of Inquiry into Human Fertilisation, Mary Warnock helped draw up the original guidelines for IVF treatment, including the stipulation that all donors should be anonymous. But now she says that changes in social attitudes have convinced her that this should be dropped.

Dr Kamal Ahuja has travelled the same road. The director of the Cromwell IVF programme at the Washington Hospital, Tyne and Wear, now favours ending the anonymity of donors.

"I used to be against it on the grounds that perhaps it might affect the supply of donors. Those who would be confronted with the situation that, 18 years on from now, someone might knock on their door, which might be frightening for some," he says.

But he says research from the United States, Scandinavia and Australia, where donors have no anonymity, which suggests donors are not deterred, has convinced him of the benefits of the move. While he opposes the retrospective lifting of anonymity, which has been ruled out by the Department of Health, he says the decision should rest on what is best for the children.

"The welfare of the children might encompass the desire to know who their procreative parents are. Society is changing. There was a fear that children who find out later in life would suffer, but I think children today are far too smart.

"This seems like a rather insignificant thing in terms of what should be kept hidden and what they should be told, and it is perhaps very significant for the children. The more questions you ask, the more comfortable you become with the idea that perhaps this information belongs to the people concerned," he says.

And he says that, since the introduction of a new treatment for couples where the man has a low sperm count, the number of couples using donor sperm has declined dramatically.

"Why treat such a small minority of people in this way by withholding information?" he asks.

Any changes in the law are also expected to address the issue of parental responsibilities. Sperm donors could be deterred by the prospect of the Child Support Agency coming knocking, but this is likely to be ruled out by any legislation.

For Ian Aird, director of the IVF unit at Gateshead's Queen Elizabeth Hospital, the issues are less clear cut, although in the end he is in favour of the change.

"It is a very difficult issue and it all revolves around the welfare of the child. The problem is that there have been studies that show a lot of men would not have donated their sperm had they had to reveal their identity.

"If the law was changed so that identifying information could be given about donors, the whole sperm donation service would be adversely affected," he says.

Mr Aird says one option is that donors could be given the choice of retaining anonymity, and couples could then have the choice of using sperm from a donor whose identity would be kept secret, or from a donor who was happy to be identified, basing their decision on how much they intended to tell their child about its origins.

"If the child isn't told how it was conceived then the whole issue of donor identification would not come up. But if the child is told, they may want to receive more information about their genetic origins," he says.

"The ideal is identifying information should be available to the offspring of sperm donors, but I do have a concern that it could limit the number of sperm donors and it may result in a total collapse of the service."

This fear is echoed by Dr Alison Murdoch, consultant gynaecologist at the International Centre for Life in Newcastle. The centre, the main IVF unit for the North-East, carried out about 700 IVF treatments last year, but only 132 using donor sperm.

But she says the number of donors coming forward could plunge if they lost their anonymity.

"Most donors donate on the premise that they're going to be anonymous, and most donors have expressed a view that if they felt they were going to be identified they would not donate.

"We're very worried that if the law is changed for everybody, we would have no donors and the children these parents are worried about would not exist," she says.

Dr Murdoch says the drive to end anonymity comes from a small number of parents who want their children to know their origins. And she says studies in other countries which suggest donors would not be deterred by being identified ignore the cultural differences in the UK.

'About 90 per cent of parents who conceived using donor sperm don't tell their children. We need to get away from the idea that it is something to be furtive and secretive about.

"When we get to the stage where the parents are able to talk freely with their children, then you are going to get donors more at ease about being identified. The way to approach it is to persuade the couples who have conceived by donor sperm to be more open," she says.

She agrees with Mr Aird that one option may be to give donors the choice of being identified or not, but says the evidence suggests this may not work.

"All the attempts that have been made to try and select people who are prepared to be identified have not been successful, and I don't have any faith that this is likely to change in the near future," she says.

"That means we are still faced with the prospect that, in the short-term, the service will close down."

And if those fears prove justified, and if donating sperm continues to be seen as a furtive activity, then it may not just be the charitable - or impoverished - students who lose out.