THE legal and ethical debate surrounding cloning has become the most complex in the medical field.

And news that a human embryo has been cloned to supply tissue for transplants means that world legislation to control this mind-boggling but perilous era in scientific development can wait no longer.

Advanced Cell Technology, the American company which has used the Internet to announce that it has produced "preimplantation embryos", aims to use them for the treatment of disease.

Of course this is exciting news for those involved in the fight against stroke, cancer, Aids and neurodegenerative disorders such as Parkinson's and Alzheimer's disease.

And who can blame those suffering from those diseases from welcoming a breakthrough which offers a ray of hope?

But while there is clear potential for good in this medical milestone, it is overshadowed by the enormous potential for bad.

It is only a matter of time before a cloned human being is born. The knowledge is there now and it will inevitably be used in unethical ways - if that isn't already happening.

We are seeing a development which previous generations would have viewed as science fiction. But the reality has potentially tragic implications.

Rogue scientists will seize the commercial opportunities to produce cloned babies and dabbling in the creation of human life is certain to lead to mutations and deformities along the way. Lives may be saved but lives will also be blighted.

Creating cloned humans may be banned by the majority of countries but a world black market will be formed and abuse will be rife.

Arguments about whether it was right or wrong for this kind of research to take place are now as futile as standing in front of an out of control train. The point of no return has been reached.

But while there is no going back, the strictest controls must be enshrined in the laws of as many countries as possible so those abuses can at least be limited. It is a sad fact of life that stopping them completely is now impossible.