Rolls-Royce, Britain’s leading manufacturing multinational, may have used bribes to land major contracts, it has emerged.

A joint investigation by the Guardian and the BBC, in which leaked documents were uncovered and testimonies were heard from insiders, found the company hired a network of agents to help it land lucrative contracts in at least 12 countries around the world.

The investigation, aired on Panorama on Monday, found the use of agents by the blue-chip manufacturer was wider than previously publicly known, with reports that in one case the Rolls-Royce made secret payments of around £10 million to an unregistered Indian agent.

The network of agents is now said to be the focus of large-scale investigations by anti-corruption agencies in the UK and the US - reportedly looking into specific allegations that the hired intermediaries were bribing people.

Rolls-Royce, which sells turbines and engines for passenger jets and military aircraft and is worth an estimated £13 billion, reportedly declined to answer detailed questions.

A spokesman for Rolls Royce told The Guardian: “Concerns about bribery and corruption involving intermediaries remain subject to investigation by the Serious Fraud Office (SFO) and other authorities. We are fully cooperating with the authorities and we cannot comment on ongoing investigations.”

The agents are reported to have been hired in at least 12 countries – Brazil, India, China, Indonesia, South Africa, Angola, Iraq, Iran, Kazakhstan, Azerbaijan, Nigeria and Saudi Arabia.

One alleged middleman for Rolls-Royce who emerged from the investigation was Sudhir Choudhrie, a businessman and arms dealer whose family has donated more than £1.6m to the Liberal Democrats.

The Guardian and the BBC understand that Choudhrie family companies were paid millions by Rolls-Royce.

Mr Choudhrie and his son, Bhanu, have been arrested and questioned by the Serious Fraud Office (SFO) over the bribery allegations. Both denied wrongdoing and were released without charge.

Labour and Conservative administrations have forged close relations with Rolls-Royce and have often lobbied foreign governments to give large export contracts to the manufacturer.

Mr Choudhrie's lawyers told the BBC he “has never paid bribes to government officials or acted as an illegal middleman in defence deals”. They said he has “no knowledge of the contents” of the list.

It was first revealed Rolls-Royce was being investigated for corruption in December 2012 when, for the first time in the company’s 106-year history, an investigation by an external law firm had “identified matters of concern” over the methods used by intermediaries in China, Indonesia and other overseas markets in the pursuit of lucrative contracts.