The Federal Court gave the investors leave on Monday to issue a subpoena to Mr Downer by November 20.

The $100 million damages suit begins on November 30.

The shareholders asked the court to order Mr Downer to appear after lawyers for the grains trader revealed during a pre-trial hearing last week that part of its defence would be that the government knew about the "transport fees" paid to Iraq while United Nations sanctions were in place.

The shareholders' solicitor, Maurice Blackburn principal Ben Slade, said yesterday that Mr Downer would be called as a witness "to refute the suggestion that AWB is making that the government knew that kickbacks were being paid".

"We feel that we had no choice but to ask the previous minister to say again what he said before the Cole inquiry," Mr Slade said.

In the final report of his 2006 commission of inquiry, Terence Cole, QC, summarised Mr Downer's evidence as "that he did not know and was not at any time aware during the period from about 1999 to 2003 of anything about" AWB's payment of fees to Jordanian transport company Alia, or Alia's connection with the Iraqi government.

"There is no evidence to suggest that minister Downer possessed any such information at any material time," he said.

The investors allege that they suffered losses when the inquiry exposed the illegal payments.

They claim this damage would not have occurred if AWB had not concealed the nature of the payments from officials because ministerial permission for its wheat shipments to Iraq would not have been given.

Justice Lindsay Foster raised the prospect during Thursday's hearing that Mr Downer would be called. The judge said he could "see some difficulties" for the shareholders in trying to "prove that the minister didn't know" without calling him.