MPs are planning a change in the law to allow babies to be conceived from artificial sperm, a move described by opponents as playing God with human DNA.

A furious debate is building over how far to leave the door open to its use in IVF treatment, ahead of a Commons vote due shortly on the government's Human Fertilisation and Embryology bill. The legislation currently allows so-called artificial gametes in research, but imposes a blanket ban on their use in creating a human pregnancy.

The technique involves the creation in a lab of sperm grown from embryonic cells taken from the would-be parent. Although the science is in its infancy, it could ultimately help people rendered infertile by cancer treatment, or fortysomething women who can no longer produce their own eggs, to have children who are genetically related to them.

A cross-party group of MPs led by Liberal Democrat Evan Harris will table an amendment to relax the ban. 'There is no good explanation for not allowing this option for people who have survived cancer and cannot have children,' Harris told The Observer. 'This is a good bill, but the government needs to recognise a few improvements are still needed - such as allowing the use of artificial gametes - before we can say the UK has rational and progressive regulation.'

Dawn Primarolo, the Public Health Minister, confirmed last night that she was considering pleas from MPs and scientists to relax the ban. There was a 'powerful argument' that the new technique could help solve a shortage of sperm donors, she said, but she was sympathetic to arguments that a decision should not be rushed.

So far pregnancies have been successfully created only in mice: of seven born alive, all died prematurely. Experts believe it could be 10 years before a human pregnancy could be safely attempted. But scientists have cultured human sperm using stem cells - immature building blocks containing DNA - taken from bone marrow.

Last night Josephine Quintavalle of the campaign group Comment on Reproductive Ethics said lifting the ban could lead to 'the ultimate incest' of an

individual trying to create both sperm and eggs from their own tissue, making them both mother and father of a child. It was 'quite ridiculous' to rely on the potential of a technique still in its infancy, she said: 'If you turn the focus around from infertile adults and think about what you are creating, you always get the perspective you should adopt. I think we are becoming extremely selfish in our attitude to the children we produce.'

Scientists however argue that research will be halted if there is no chance of being able to use the technique in IVF treatment. Dr Allan Pacey, secretary of the British Fertility Society, said ministers had not properly explained why they wanted a ban: 'I think if you talk to people - take the example of a cancer victim who hasn't got any sperm or eggs because they've had chemotherapy - if you get to the step where we could make it for them, most people will say they can see the benefits,' he said.

Although the bill allows for research Pacey said 'nobody is going to be able to convince a UK funding organisation to fund research in this area' unless it could ultimately be used in treatment.

Harris's amendment would add a so-called regulation-making power to the bill, a device ensuring that if the new technique were proven safe for humans, MPs could nod through a decision allowing it to be used in IVF without a full parliamentary debate and vote. It would also stipulate that the gametes should come from two halves of a couple, ensuring the technique could not be used for a single parent to become both mother and father to the same child.

The approach is expected to be backed by the British Medical Association, the Medical Research Council and the Royal College of Obstetrics and Gynaecology.

Primarolo said she was still consulting on the issue, but added: 'The research can be done, and the issue is whether we legislate to say if it were successful it could proceed. There are some who are saying - and I think these are strong arguments - that it does raise some profound ethical questions.'