Defence Secretary Geoff Hoon and government media director Alastair Campbell have been re-called and will be quizzed on Monday about a pre-war Iraqi weapons dossier and their handling of a scientist who questioned its central claim.
The inquiry into the suicide of weapons expert David Kelly has already wreaked political damage on Tony Blair's government.
Campbell and Hoon are likely to be asked about the government's handling of Kelly after he admitted he may have been the source of an explosive BBC report accusing Blair's government of "sexing up" the dossier.
Hoon, singled out by British media as a likely government fall guy over the Kelly affair, has played down his role in the strategy to name the scientist.
But the inquiry has shown he attended a meeting where officials at his ministry agreed to confirm Kelly was the suspected BBC source if his name was put to them by journalists.
He also overruled advice from his top civil servant to shield Kelly from a hostile parliamentary grilling, just days before he took his life.
Lawyers for Kelly's family have their first chance to quiz Hoon over both issues on Monday.
Meanwhile, Campbell may be asked by the inquiry why he asked a senior intelligence officer to harden up an assertion that Iraq could deploy weapons of mass destruction at 45 minutes notice.
Geoff Hoon factfile
Born 6 December 1953
First career as barrister
Became MP in 1992
Apponted defence minister in 1999
One of Blair's most trusted lieutenants
Last week, Blair's ruling Labour Party lost its first parliamentary by-election in 15 years, a stinging setback which reflected the collapse of public trust triggered by revelations at Lord Hutton's inquiry into Kelly's death.
Before Monday's cross-examination an opinion poll found one in three British voters thought Hoon should resign over his role in the affair.
The survey of 2000 adults, conducted for the Financial Times by research group Mori, showed one in five felt Blair should quit also.
To overcome anti-war sentiment within Labour, Blair based his case for joining the US invasion of Iraq on the "serious and current threat" from Baghdad.
But five months after the war no chemical or biological weapons have been found in Iraq.
Counsel to Hutton's inquiry James Dingemans will deliver a closing statement on Thursday.
But for Blair, the long wait for a final verdict will stretch on at least until November.