The Liberal Democrats have called for the records of correspondence between Downing Street and Sue Gray over her inquiry to be made public, including emails, letters and messages.
It comes amid reports Number 10 put pressure on Sue Gray to water down the report and omit key names and details.
The Liberal Democrats also said any correspondence should be handed over to the Privileges Committee investigation into Boris Johnson lying to Parliament.
Liberal Democrat Deputy Leader Daisy Cooper said: “Brandon Lewis’ half-hearted denial that Downing Street tried to water down the Sue Gray report simply isn’t good enough.
“Boris Johnson has lied time and again to try and cover up his law-breaking parties and pull the wool over people’s eyes.
“We can’t trust a word he or his Conservative colleagues say.
“The only way to get to the truth is to make public any correspondence between Downing Street and Sue Gray over her report.
“People are sick of Boris Johnson’s cover ups and lies, they deserve full transparency now.”
Responding to reports that Downing Street lobbied Sue Gray to dilute her report on lockdown parties Liberal Democrat Chief Whip, Wendy Chamberlain MP commented: “This looks like another disgraceful attempt by Boris Johnson and the Conservatives to cover up for their lies and law breaking.
“The Privileges Committee must immediately look into the supposed interference into the publication of the Sue Gray report.
“If the government really did alter the report, the British public should be told the truth.”