Civil service chief Simon Case has been blocked from appearing before MPs next week as ministers brace for Sue Gray's Partygate report.
The Cabinet Secretary and Government ethics chief Darren Tierney had been due to give evidence to the Public Administration and Constitutional Affairs Committee (PACAC) about propriety of governance in the wake of the Greensill lobbying scandal.
MPs had been due to raise the Partygate saga at the session, along with proposed job cuts to the civil service.
But their appearance at the hearing, which was confirmed several weeks ago, has now been postponed until June 28.
The committee was told by officials in the Cabinet Office that ministers no longer deemed it appropriate due to "recent events".
Tory PACAC chairman William Wragg said: "The session with the Cabinet Secretary was an important one considering the number of propriety and ethics issues on the agenda.
"We had also hoped to get clarity on the Government's plans for civil service reform, public scrutiny of which was much-needed after they were briefed to the press last weekend.
"The intervention to pull the session at such short notice evades timely parliamentary scrutiny of these plans and puts government transparency in a poor light."
Mr Case was originally tasked with investigating reports of lockdown-flouting parties in No10 and Whitehall but he stepped aside when it emerged one of the events was held in his office.
He reportedly told colleagues he was worried about receiving a Partygate fine but he is not understood to have been among the 83 people who received penalties.
The Metropolitan Police wrapped up their probe on Thursday after handing out 126 fixed penalty notices for lockdown-flouting parties.
Boris Johnson avoided receiving further fines beyond the penalty he received in April over his surprise lockdown birthday bash in June 2020.
But Downing Street is bracing for senior civil servant Sue Gray's Partygate report, which is due to be published next week.
Her interim report in January slammed a “failure of leadership” at the top of Government and is expected to be highly critical of the culture in Downing Street during the pandemic.
