In November last year, Britain's Serious Fraud Office (SFO) said it had launched a joint investigation with its French counterparts into "suspected bribery and corruption" at the multinational, which denies any wrongdoing.

A 41-year-old management controller, who worked at the company between August 2018 and June 2023, was the whistleblower who alerted the authorities and caused the probe to be opened, according to two sources following the case who requested not to be named because not allowed to speak to the press.

The former member of staff, who wishes to remain anonymous and who AFP reached through his lawyer, said he started asking colleagues questions after he noticed suspicious orders on the margins of big air defence deals with Indonesia and Saudi Arabia.

He said that in late 2018 he noticed a curious payment order for a service worth £400,000 ($520,000 at today's rate) on the sidelines of a deal between Thales UK and Indonesia.

He said he grew suspicious when someone asked him for a retroactive approval of the order with incoherent documents produced after it was made, and reported this to his superiors.

"The only thing I was told was to keep quiet," he said.

He alleged that months later, he noticed another £100,000 transferred to Saudi Arabia, where a contract had also been signed.

He said he alerted colleagues in writing and orally, then via an internal complaint platform in 2022.

He believes this is why he was fired.

Thales told AFP the former employee only filed an internal complaint "several hours after being summoned to a meeting towards a possible dismissal for professional incompetence".

A team of in-house auditors led an internal probe and concluded that there were no grounds to his allegations, it said, adding however that it was cooperating with the British and French authorities.

Neither the SFO nor the French financial prosecutor's office wished to comment on an ongoing investigation.

One source following the case said the Indonesian contract was being investigated in the joint probe.

But no source confirmed or denied that any Saudi contract was also being examined.

A judicial source, also wishing to remain anonymous, said the French investigators were looking at an "arms market" in Asia, without saying which country was involved.

The French judiciary is looking into at least five other cases of alleged graft involving the defence firm.

An investigating magistrate is investigating the sale of submarines to Malaysia in 2002 and could order a trial against parties including the firm.

Four other preliminary probes, launched between 2016 and 2023, are looking at alleged corruption in places including Brazil, India and the United Nations. 

No charges have been pressed against Thales in those investigations.

Thales told AFP the probes were ongoing and that it "strictly follows national and international regulation".