Peter Garrett, research director at the anti-abortion charity Life, said: "Once you open the flood gates on the production of human cloned embryos, you are setting up the preconditions for full pregnancy cloning.
Supporters of the change say it could help scientists find cures for a range of diseases that are presently untreatable. But the decision has also raised ethical concerns about how the sanctity of life will be affected.
Researchers believe these embryonic cells will revolutionise the treatment of degenerative diseases, such as Alzheimer's and Parkinson's, particularly when the cells are obtained using the cloning technology that produced Dolly the sheep.
The vote by MPs to relax existing rules had a two-thirds majority, with 366 members voting for the change and 174 against.
The highly controversial nature of so-called therapeutic cloning and embryo experimentation in general, meant MPs were given a free vote on an amendment to the 1990 Human Fertilisation and Embryology Act.
'Slippery slope'
Strong lobbying from outside interest groups had ensured the debate was a high-profile occasion.
Peter Garrett, research director at the anti-abortion charity Life, said: "Once you open the flood gates on the production of human cloned embryos, you are setting up the preconditions for full pregnancy cloning.
"My view is that we are only a couple of years away from cloning human beings."
But public health minister Yvette Cooper made an impassioned plea for scientists to be given the go-ahead for stem cell research, denying it was a "slippery slope" to full human cloning.
Ms Cooper told the Commons that the research could hold "the key to healing within the human body", giving hope not only to those suffering from a wide spectrum of degenerative diseases.
Tough rules
Shadow health secretary Liam Fox said he was morally against the use of embryo cells and had not been convinced there was no alternative. But it was unrealistic to think, he said, that such research could be halted and so tough rules were needed to set the moral boundaries.
Liberal Democrat health spokesman Nick Harvey said he had weighed the arguments carefully and would support the research so that help could be given to those suffering the "slow death" of degenerative diseases.
Labour's Anne Begg told the House it had a duty to pass the amendment.
Stem cell research would enhance our ability to treat the most "heart-rending conditions that are presently untreatable," said the Aberdeen South MP, who suffers from a genetic brittle-bone condition.
15 David Beckhams
Labour MP Dr Howard Stoate said he was in no doubt that the Commons should approve the measures.
"As a doctor I see all parts of the spectrum of human misery right from the infertile couple to the aged person suffering from Alzheimer's."
But Labour's Dr Ian Gibson retorted: "Would you tell me why we shouldn't produce 15 David Beckhams that I could use in the Parliamentary football team and 659 Betty Boothroyds to service this place and the public?"
Liberal Democrat's Evan Harris said it was important to bear in mind that the consent of egg donors would be needed before any research could be carried out. Tory MP Edward Leigh said he realised his opposition to the measures would mean having to answer questions on his motives from people who suffer "appallingly" from degenerative conditions.
But although he accepted embryonic research was the most effective at the moment, he warned it was effectively giving the green light to cloning human beings.
Summing up the debate, Ms Cooper paid tribute to MPs for "the most thoughtful and considered debate" she had witnessed in the House.