One of the corrupt British brothers at the heart of a vast cash-for-contracts scandal in the oil and gas industry has been jailed for just a year after cooperating with US prosecutors.

Saman Ahsani, the former chief operating officer of Monaco-based Unaoil, was sentenced in Houston, Texas, on Monday for his role in running a system to help western companies win projects in the Middle East for nearly two decades.

The 27 companies included engineering giant Rolls-Royce and Dutch-based SBM Offshore, with millions of dollars in bribes paid to officials in Iraq to secure offshore mooring contracts for oil tankers and other infrastructure after the downfall of Saddam Hussein.

Details of the corruption came in a leak to Australian newspaper The Age in 2016, sparking a series of investigations around the world.

The pursuit of Ahsani and his older brother, ex-chief executive Cyrus, sparked a bitter dispute between prosecutors in the US and the UK, which also wanted to put them on trial. One British investigator was sacked after branding a US counterpart a “quisling” in a stormy session at a London pub.

Ahsani was originally detained in Italy in 2018 under an arrest warrant secured by the UK but he was eventually whisked away to the US where he secured a plea deal that resulted in his light sentence. His brother is due to be sentenced later this year.

They both pleaded guilty in 2019 to broking corrupt deals involving millions of dollars in bribe payments to officials in countries including Iran, Iraq, Kazakhstan, Libya and Syria.

US court documents showed that Ahsani will be returned to his home country on completion of his jail sentence.

The UK’s white collar crime body, the Serious Fraud Office (SFO), secured a series of convictions of men linked to bribing officials to win oil tanker mooring and other contracts in Iraq worth $1.7bn. But convictions against three of the men were later quashed.

The US head of the SFO Lisa Osofsky was heavily criticised in a subsequent report following the failed prosecutions over her meeting with a fixer acting on behalf the Ahsanis, who had helped to broker the plea deal with the United States.

SBM agreed to pay $238m in 2017 to US authorities over its connection with bribery schemes in Brazil, Angola, Equatorial Guinea, Kazakhstan and Iraq.