British defence equipment firm BAE Systems could face criminal charges if efforts to force the company to accept a deal with corruption investigators fails, a source said late Wednesday.

The Serious Fraud Office has been trying to persuade the company to accept a plea deal rather than face prosecution over claims it paid millions of pounds to win contracts in Africa and elsewhere, the source said.

The deadline for a deal, that could include a large fine, is midnight Wednesday. An announcement from the SFO is expected as early as Thursday.

The SFO could apply to Attorney General Patricia Scotland for permission to bring charges against BAE if the company refuses the US-style plea bargain.

BAE said it is co-operating with the authorities as part of a policy of "allowing the ongoing investigations to run their course," the Financial Times reported on its website. The company declined to comment further.

"There are still ongoing discussions between us and the company," an SFO spokesman was quoted by Dow Jones newswires saying.

BAE has repeatedly denied allegations that it paid hundreds of millions of pounds of bribes to win contracts in Tanzania, South Africa, Romania and other countries.

One of the world's biggest arms makers, the company generates 58 percent of its sales in the United States and is the sixth-largest supplier to the US defence department.

The SFO was embroiled in controversy in 2006 when investigators ditched a probe into a BAE deal with Saudi Arabia worth 43 billion pounds (54 billion euros, 85 billion dollars).

Then prime minister Tony Blair explained the decision by saying the investigation could threaten intelligence links at a key point in the "war on terror". The decision was criticised by anti-corruption campaigners and the British press, which accused the government of bowing to pressure from Riyadh.