Former Rolls-Royce boss Sir John Rose has been questioned under caution by the Serious Fraud Office as the investigation into bribery at the engineering business steps up.

Last month the FTSE 100 engineering giant agreed to pay £671m in fines after an international investigation led by the SFO into corruption at the company.

Rolls secured a "deferred prosecution agreement" (DPA) under which it did not face criminal charges but admitted instances of bribery.

In his judgment on the company's actions - which included using middlemen to pay bribes in almost a dozen countries - Lord Justice Brian Leveson referred to the "most serious breaches of criminal law in the areas of bribery and corruption".

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He added that some of these "implicated senior management and, on the face of it, controlling minds of the company".

The judgment said part of the reason that Rolls secured a DPA was that management at the time of the bribery had been cleared out and that Rolls was a different company now.

Had it faced criminal charges, Rolls could have been banned from doing business in many countries, wiping out a huge chunk of its £75bn order book.

Sir John led the FTSE 100 company from 1996 to 2011, a period when several of the offences took place.

Lord Justice Leveson's judgment said Rolls knew about corruption claims in 2010 but did not inform anti-graft regulators.

Being questioned under caution would have involved Sir John's being read his rights, and is a different process from the SFO's questioning of witnesses.

Sir John is not the only person to have been questioned under caution, and it is understood that "dozens" of those involved at all levels have been quizzed.

Sir John, who is being represented by law firm Wilmer Hales, has denied any wrongdoing.

An SFO spokesman said: "We cannot comment on an ongoing investigation."