The controversial fertility expert, Professor Panos Zavos, is expected to make an announcement about his work on human cloning on Saturday.
Last year, the professor claimed to have cloned a human embryo, but sceptics said he had not published enough proof.
Mystery surrounds the one-day visit to the UK but he is understood to be ready to implant a cloned embryo.
Reproductive cloning is illegal in the UK.
Genetic material
The professor is teaming up with the British doctor Paul Rainsbury who has controversially helped send couples to choose the sex of their baby in America.
On Saturday they are expecting to announce another highly controversial project, the splitting of embryos.
Half would be transplanted into a woman to become a child and the other half stored to provide genetic material in case the child needed it later in life.
The professor is holding a press conference in London to announce the latest details of his cloning research.
He is expected to announced that he is looking for a surrogate mother for a cloned embryo and will say that several women have already volunteered.
Critics say human cloning should not go ahead at all.
They say it is unethical to clone humans, because animal experiments have led to many failures and a high rate of abnormalities in those pregnancies which do result in live births.
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