A British tycoon is identified by US diplomats as the man at the centre of one of America's worst recent corruption scandals, in which large bribes were allegedly handed over in the ex-Soviet state of Kazakhstan.

Robert Kissin, a UK banker and commodity trader, is alleged to be the key middleman who handled a $4m (£2.5m) secret payment.

According to leaked US diplomatic dispatches released by WikiLeaks, the cash was moved through a Barclays bank account set up in London on behalf of an offshore shell company registered in the Isle of Man, where true ownerships are easier to conceal.

The money was designed to help Texas oil services company Baker Hughes make corrupt payments to Kazakh state oil chiefs in return for a lucrative $219m contract, according to the company's subsequent admissions.

After being found out, Baker Hughes eventually paid a total of $44m in penalties to the US authorities, following charges under the Foreign Corrupt Practices Act. At the time, in April 2007, it represented the highest-ever such penalty obtained in Washington by the department of justice and the Securities and Exchange Commission (SEC), and marked the beginning of a major US crackdown on overseas bribery.

Speaking at his London office at Lewis & Peat Oil and Gas, Kissin told the Guardian: "I was employed by Baker Hughes. I was involved, but that's it – it's an old story. There are a number of inaccuracies in this account but I'm not going to go into it."

The published plea agreements at the time referred to a "British connection", under which payments were made through the London financial system and the Isle of Man offshore entity. But Kissin's name was withheld.

Baker Hughes's local manager at the time was another Briton. He was named as Roy Fearnley, originally from Huddersfield. He arranged for an agent or go-between to be hired, according to the company's confessions.

The SEC said at the time: "Baker Hughes retained the agent principally at the urging of Fearnley … Fearnley told his bosses that the 'agent for Kazakhoil' told him that unless the agent was retained, Baker Hughes could 'say goodbye to this and future business'."

The US authorities described the unidentified British agent at the time as a co-conspirator.

Shortly before the court settlement was announced, company executives privately explained to the US ambassador in Kazakhstan that the British agent hired by them in September 2000 was "the son of Lord Kissin" according to a confidential cable on 11 April 2007.

Kissin, 63, is the son of the late east-west commodity trader and Labour donor Harry Kissin, who was controversially made a peer by prime minister Harold Wilson in 1974. He was one of the circle of Wilson acquaintances with eastern European links who were spied on by MI5 without result during Wilson's premiership, according to MI5's official history.

Kissin followed in his father's commodity trading footsteps.

After the disintegration of the Soviet Union, he was quick to cultivate relations with the newly independent state of Kazakhstan.

In 1991, as director of the Kazakhstan Trade and Development company, he was reported to have hired PR man Tim Bell's lobbying firm, Lowe Bell, to promote an official visit to Britain by President Nursultan Nazarbayev.

Kissin keeps a flat in Cadogan Place, Knightsbridge, but lists his current address on company documents as the tax haven of Monaco.