LONDON, June 10, 2005 -- A millionaire British businessman, Friedhelm Eronat, was named last night as the purchaser of oil rights in the Darfur region of Sudan, where the regime is accused of war crimes and where millions of tribespeople are alleged to have been forced to flee, amid mass rapes or murders. The disclosure was greeted with outrage by human rights campaigners. "From a moral point of view these people are paying a government whose senior members may end up in front of the international criminal court for war crimes," Simon Taylor, director of Global Witness, said yesterday.

A London representative of the Darfur rebels last night called for oil exploration to stop until there was a peace settlement. "The only beneficiaries are the ruling elite," Ahmad Hussein Adam told Channel 4 news. "This is going to support their military campaign against our people."

Documents seen by the Guardian suggest that Mr Eronat, who lives in a £20m house in Chelsea, swapped his US passport for a British one shortly before the deal was signed with the Sudan regime in October 2003.

US citizens are barred from dealing with Sudan under sanctions dating from 1997.

The disclosure that Britain is serving as a base for question able African oil transactions comes in the run-up to the July G8 summit at Gleneagles, at which Tony Blair's central theme will be the need to help Africa.

The documents show that Mr Eronat may have been acting for China, which has been prominent in the new "scramble for Africa" and its oil deposits. Two Chinese corporations were given an option to buy 50% of Mr Eronat's newly acquired stake in the Darfur field. The option expired last year. It is not known whether China took it up.

Mr Eronat's lawyer said yesterday that he "has purchased no oil concessions in Sudan ... and Mr Eronat has no interest" in the oil concession.

An initial $3m was paid to the Sudan regime for exploration rights, shared with the state oil company and some other Sudanese interests.

Mr Eronat, who is reputed to be worth £100m, has made a fortune out of oil deals, mainly through his offshore Cliveden Group. He was accused by Global Witness last year of being the owner of a Swiss company allegedly used as a conduit to pass millions of dollars from Mobil Oil to the president of Kazakhstan. A trial is pending in the US of a banker involved in those transactions. Mr Eronat was not charged with any offence.

The Islamist regime in the largely Arab north of Sudan has become an international pariah because of long-running attempts to crush rebellions in the south and more recently in Darfur in the west.

A peace agreement in the south included agreements to divide up oil revenues, but the deal provoked a second rebellion in the adjoining Darfur region, which began in spring 2003. The military regime's violent response is estimated to have caused more than 1.5 million people to flee.

The international criminal court says it is considering bringing charges of war crimes and possible genocide against government officials in Sudan.

Announcing a formal investigation into the murders, rapes and massacres that have taken place in recent years, a spokesman for the court said evidence was being gathered and a list of suspects would be drawn up.

A UN commission of inquiry said there had been serious violations of human rights. The UN has forwarded a list of more than 50 suspects to the ICC.

Mr Eronat's London lawyer, John Reynolds of McDermott Will & Emery, said yesterday: "Mr Eronat has purchased no oil concessions in Sudan." He said the oil exploration group had various shareholders, of which Cliveden Petroleum Sudan Ltd was only one.

"Are you alleging that killing has taken place in [the] concession acreage?" he asked.

The company documents seen by the Guardian show that at the time of the 2003 sale, Mr Eronat confirmed that he was the sole owner of Cliveden Sudan, registered offshore in the British Virgin Islands with bearer shares and no register of ownership.

The documents state that Cliveden Sudan in turn bought the largest single share in the oil exploration concession from the Sudan regime on October 21 2003.

The disclosure of Mr Eronat as the man behind the Darfur deal followed a dispute between him and the former chairman of one of his companies, the lawyer Peter Felter.