Four senior managers at a multinational oil firm have been accused in a court document of taking part in a scheme to pay multimillion-pound bribes to land contracts.

The accusation has been made by the Serious Fraud Office, which is investigating suspected corruption and money laundering involving the multinational Petrofac.

The allegation was made in a charging document filed in criminal proceedings against David Lufkin, a former Petrofac executive who pleaded guilty to bribery this year.

The SFO alleges that the quartet of senior managers acted with Lufkin. No charges have been laid against the four executives, and being named in the indictment does not constitute evidence of their involvement or any proof of guilt.

Petrofac and one of the four said they were concerned that they had been identified in the charges against Lufkin by the SFO without any attempt by the prosecutors to interview or speak to them.

“This is materially prejudicial to the rights and reputation of our people and the company, and also denies them any opportunity to answer the allegations,” said a Petrofac spokesperson, who added that the four executives retained the firm’s full trust and confidence.

Petrofac was co-founded by Ayman Asfari, a donor to the Conservative party. He and his wife have given almost £800,000 to the party since 2009. He is Petrofac’s major shareholder and chief executive.

In May 2017 he was arrested and interviewed under caution by the SFO and released without charge. He has not been charged with any offence and is not named in the charges against Lufkin.

David Cameron appointed Asfari in 2014 to be one of the government’s “business ambassadors”, given the task of “promoting the UK’s excellence internationally”. The initiative was ended this year.

With offices in 24 countries and employing more than 11,000 people, Petrofac designs and constructs facilities for the oil and gas industry, receiving revenues of more than £5bn last year.

However, its share price crashed upon the announcement of the SFO investigation in 2017 and has struggled to recover since.

In February, Lufkin, 51, previously global head of sales for Petrofac International Limited, pleaded guilty to 11 counts of offering bribes between 2011 and 2016 in an attempt to secure contracts in Saudi Arabia worth £2.7bn and contracts in Iraq worth £566m. Lufkin has yet to be sentenced.

In the detail of the charges against Lufkin, the SFO names the four senior managers – George Salibi, ES Sathyanarayanan, Mani Rajapathy and Paolo Bonucci – and alleges they acted with Lufkin.

A lawyer for Salibi said he “emphatically denies any suggestion of wrongdoing. He is dismayed at the SFO’s wrongful naming of him, in circumstances where he has never been charged with any offence, nor even spoken to, let alone interviewed, by the SFO in relation to any aspect of the charge on which he is named.”

Sathyanarayanan, Rajapathy and Bonucci declined to comment.

A Petrofac spokesperson said: “No charges have been brought against any Petrofac group company or any serving officers or employees since this investigation began. Since February we have conducted extensive additional investigations and have not found – nor been provided by the SFO with – any evidence to support the naming of any employees in those charges. On this basis, they continue to have the full trust and confidence of the company.

“We find it concerning that some individuals have been named in the charges against David Lufkin without any attempt being made by the SFO to interview or speak to them. This is materially prejudicial to the rights and reputation of our people and the company, and also denies them any opportunity to answer the allegations. Notwithstanding this, we continue to engage with the SFO to aid their work and support them in bringing this investigation to conclusion with pace and focus.”

Petrofac’s co-founder Maroun Semaan is also named in connection with six of the counts against Lufkin. Semaan died in 2017. His family have denied his involvement in any wrongdoing and he was not arrested or interviewed.

The SFO said it could not comment as the two-year investigation into the alleged unlawful use of agents in a number of countries continued.