British lawmakers voted Monday to approve controversial plans to allow the use of animal-human embryos for research.

The proposed laws, the first major review of embryo science in Britain for almost 20 years, have provoked stormy debate — pitting Prime Minister Gordon Brown and scientists against religious leaders, anti-abortion campaigners and a large number of lawmakers.

Brown has said he believes scientists seeking to use mixed animal-human embryos for stem cell research into diseases such as Parkinson's and Alzheimer's are on a moral mission to improve — and save — millions of lives.

• Click here for FOXNews.com's Patents and Innovation Center.

The process involves injecting an empty cow or rabbit egg with human DNA. A burst of electricity is then used to trick the egg into dividing regularly, so that it becomes a very early embryo, from which stem cells can be extracted.

Scientists say the embryos would not be allowed to develop for more than 14 days, and are intended to address the shortage of human embryos available for stem cell research.

By allowing such mixed embryo experiments, Britain is expected to maintain its reputation as a leading center for stem cell research.

Unlike the United States, where such research is tightly controlled, British scientists say the progressive environment in the U.K. has led to many firsts, including the world's first test tube baby and cloned animal.

Legislation in Britain might also influence other European countries where such research is pursued. Chinese laws on stem cell and embryology research also closely mirror those in Britain.

"I believe that we owe it to ourselves and future generations to introduce these measures, and in particular, to give our unequivocal backing within the right framework of rules and standards, to stem cell research," Brown wrote Sunday in an op-ed piece for The Observer newspaper.

But opponents warn that an easing of laws on creating the embryos could lead to the genetic engineering of human beings.

Legislators voted 336 to 176 against a proposed ban on research using animal-human embryos and by 286 to 223 against a separate proposal covering a specific type of animal-human embryos.

Human Genetics Alert, a science watchdog in favor of the ban, claims the laws could lead to the creation of genetically modified "designer babies."

"Once we start down the road to human genetic modification, it will be very difficult to turn back," the group warned in a briefing paper for lawmakers.

Opposition Conservative lawmaker Edward Leigh, who tabled an amendment seeking to ban the practice, said the technique was a step too far for science.

"In many ways we are like children playing with land mines without any concept of the dangers of the technology that we are handling," he said in the House of Commons.

Britain's Human Fertilization and Embryology law, which regulates all stem cell and embryology research, was drafted in 1990. Brown has said it must be completely redrawn to take account of scientific advances.

Debate on other aspects of the bill are to be debated Tuesday. A final vote is expected in the coming weeks.