Rebekah Brooks and Andy Coulson are expected to make embarrassing revelations about British politicians' attempts to woo Rupert Murdoch's newspapers when they appear before the Leveson Inquiry this week.
The former News International executives' potentially explosive evidence could overshadow David Cameron's efforts to relaunch the coalition's programme after bruising local election results for the Conservatives and Lib Dems.
Mrs Brooks is likely to disclose further details about her close relationship with the Prime Minister, while Mr Coulson will speak about how he came to be appointed the Tories' top spin doctor.
Eight Cabinet Ministers - including Mr Cameron, Deputy Prime Minister Nick Clegg and Culture Secretary Jeremy Hunt - were last week given the right to see Leveson Inquiry documents and witness statements in advance. Lord Justice Leveson agreed to make them "core participants", people who have a significant interest in the hearings or may face criticism.
Mr Cameron and Mr Clegg are expected to relaunch the coalition's agenda at a joint Downing Street press conference on Tuesday ahead of the Queen's Speech on Wednesday.
But Mr Coulson's appearance before the press standards inquiry on Thursday will revive awkward questions about the Prime Minister's decision to make the former News of the World editor his communications director.
Mr Cameron said last July that "with 20:20 hindsight" he would not have hired Mr Coulson in May 2007, four months after he resigned from the Sunday tabloid over the jailing of royal reporter Clive Goodman for phone hacking.
Mr Coulson, 44, became Downing Street's communications chief in May 2010 but quit eight months later, saying controversy over the hacking scandal was making his job impossible. His Leveson Inquiry evidence will be the first time he has spoken publicly since being arrested by Scotland Yard on suspicion of phone hacking and corruption last July. He was bailed and has not been charged.
Mrs Brooks, 43, edited the News of the World and The Sun before becoming chief executive of Mr Murdoch's UK newspapers division News International in September 2009.
She and her racehorse trainer husband Charlie are key members of the influential Chipping Norton set, which also includes Mr Cameron and his wife Samantha, Top Gear presenter Jeremy Clarkson, and Mr Murdoch's daughter Elisabeth and her PR guru husband Matthew Freud. The inquiry has already heard that Mrs Brooks regularly met Mr Cameron and other top politicians along with Rupert and James Murdoch.