By Jill McGivering
Top British transplant surgeons have accused China of harvesting the organs of thousands of executed prisoners every year to sell for transplants.
Chinese officials have denied the allegations
In a statement, the British Transplantation Society condemned the practice as unacceptable and a breach of human rights.
The move comes less than a week after Chinese officials publicly denied the practice took place.
In March, China said it would ban the sale of human organs from July.
The British Transplantation Society says an accumulating weight of evidence suggests the organs of thousands of executed prisoners in China are being removed for transplants without consent.
Professor Stephen Wigmore, who chairs the society's ethics committee, told the BBC that the speed of matching donors and patients, sometimes as little as a week, implied prisoners were being selected before execution.
Chinese officials deny the allegations.
Just last week a Chinese health official said publicly that organs from executed prisoners were sometimes used, but only with prior permission and in a very few cases.
But widespread allegations have persisted for several years - including from international human rights groups.
Professor Wigmore said: "The weight of evidence has accumulated to a point over the last few months where it's really incontrovertible in our opinion.
"We feel that it's the right time to take a stance against this practice."
The emergence of transplant tourism has made the sale of health organs even more lucrative.
Patients increasingly come from Western countries, including the UK, as well as Japan and South Korea.
Professor Wigmore described this as quite widespread and growing. He and his colleagues, he said, had all seen cases of British patients who had considered going to China for transplants. He really hoped, he added, that people would think very hard about whether they should.
Secrecy surrounding executions in China has always made it difficult to gather facts.
The Chinese authorities recently announced steps to tighten regulations. From July, selling organs will be illegal and all donors must give written permission.
But the practice is lucrative and critics say much will depend on how well those rules are implemented.