David Cameron has faced demands from Labour to appear before the Commons on the Adam Werritty affair.
The findings of an official report into resigned defence secretary Liam Fox's links with Mr Werritty are expected to be published later on Tuesday.
Cabinet Secretary Sir Gus O'Donnell is said to have found that Dr Fox breached the Ministerial Code of Conduct but did not gain financially from the relationship.
It is unclear whether the report will be published in full or whether some details will be redacted.
However the Labour frontbench is to call for the Prime Minister to make a statement to MPs about contacts between Mr Werritty - a close friend and self-styled adviser of Dr Fox - and all Government ministers.
"David Cameron must come to the Commons to make clear the full extent of the links between his ministers and Adam Werritty's activities," a Labour source said. "It is time for full transparency."
Dr Fox finally resigned on Friday amid a welter of allegations suggesting his close contacts with his best man and former flatmate breached Whitehall rules. Sir Gus was ordered by the Prime Minister to take over an internal Ministry of Defence (MoD) inquiry in an effort to provide answers to "all remaining questions".
An interim MoD report has already established that the then defence secretary had met Mr Werritty - who handed out business cards describing himself as Dr Fox's adviser even though he had no official role - 40 times since coming to office.
Sir Gus is not expected to make recommendations on ministers' contacts with lobbyists, as his remit was limited to establishing the facts about Mr Werritty's activities.
Labour leader Ed Miliband is to table an urgent question in the House calling for the Prime Minister to make a statement on Sir Gus's report, a source said.