BAE Systems was told on Wednesday by the Serious Fraud Office that it is now part of a widening investigation into possible false accounting in its contracts with two marketing and travel companies that worked for the defence group on its highly-profitable Saudi Arabian business.

The disclosure raises the likelihood that executives at BAE, who up to now have not been questioned as part of the inquiry, will face interrogations by the SFO. The SFO declined to comment on the announcement.