The privileges committee inquiry into whether Boris Johnson misled the Commons may be delayed until January, after No 10 finally handed over a cache of evidence relating to Partygate four months after it was requested. The Guardian understands that the autumn target for beginning oral evidence sessions, in which the former prime minister will be called as a witness, has been abandoned. Instead, sources said the highly anticipated sessions could be pushed back to after Christmas. The delay has been blamed on the Cabinet Office digging its heels in and resisting providing key information requested four months ago. Last Friday, what was described as a “hefty chunk” of documents were handed over to the committee. A range of information – including the former prime minister’s diaries, event email invites, No 10 entry logs, briefing papers and WhatsApp messages – were originally sought in July. The seven-member committee, which has a Tory majority but is chaired by Labour’s Harriet Harman, is expected to investigate whether Johnson misled parliament by denying any Covid laws were broken. MPs had hoped to begin hearing oral evidence from as early as October but they are only now beginning to sift through the bulk of the evidence handed over by the government. With only three full sitting weeks before the Christmas recess, there are doubts about whether all of the evidence sessions can be completed before the festive break. Members of the committee are now discussing whether to push the evidence sessions into the new year, when there will be more time to examine the witnesses. “The worst thing that could happen is the committee invites a witness in and then more evidence emerges afterwards we’d like to have questioned them about,” said one source. MPs on the committee are going through the evidence line by line and may to go back to No 10 and the Cabinet Office with further requests for information. A spokesperson for the committee said it had been meeting every week in which the Commons had sat since June to “establish processes, collect and analyse the evidence”. They said: “The committee has been in continued conversation with the government to obtain evidence for the inquiry. It requested material from the government in July, which was supplied in full last Friday.” The spokesperson added that MPs were “committed to progressing the inquiry expeditiously”. The Guardian revealed earlier this month that the Cabinet Office and No 10 were refusing to hand over crucial information, and redacting details such as pass logs. Some of the initial information provided to the committee was believed to have been redacted to such an extent that crucial details were missing, leading to repeated attempts to extract more details. At the time, government insiders said there was no set date when they were obliged to respond to ad hoc requests for information or documents from a select committee. While the wait for oral evidence sessions continues, MPs are weighing how to balance the need for transparency to ensure confidence that their inquiry is being conducted fairly with the potential need to protect whistleblowers. Some evidence sessions could be held in private to protect identities where the committee deems necessary, with the account written up and released afterwards. Photographers may be barred from some public evidence sessions to avoid causing witnesses distress. One source said the evidence was likely to be taken in lengthy sessions on consecutive days lasting for about three weeks.