Amec Foster Wheeler under investigation by Serious Fraud Office

The company insisted it did not expect the probe to have an impact on its takeover by John Wood Group, which it said was still expected to take place in the fourth quarter of this year.

For its part, Wood said "it is not possible to estimate reliably what effect the outcome of this matter may have on Amec Foster Wheeler".

But Amec said it "takes its obligation to conduct business ethically very seriously and has in place a robust global anti-bribery programme, including a detailed code of conduct and anti-bribery and corruption policies" and that it "continues fully to co-operate with and assist the SFO".

The Unaoil scandal has also dragged in fellow FTSE 250 group Petrofac.

The US financial regulator, the Securities and Exchange Commission, and Department of Justice already have ongoing investigations into Amec Foster Wheeler in connection with these matters and Amec warned investors in May it believed this may well develop into an investigation of Amec by the SFO.

Wood Group’s circular to revealed it has launched an internal investigation into its own dealings with Unaoil, with the circular saying one of its joint ventures "engaged Unaoil and that the joint venture made payments to Unaoil under agency agreements".