The prime minister is among around 30 people who have been told by Ms Gray, a senior civil servant, that her report is likely to name them – with a deadline of Sunday evening to lodge any objections.
Publication is expected on Tuesday or Wednesday, after the Metropolitan Police announced the conclusion of its investigation with a total of 126 fines issued to 83 people.
Angela Rayner, Labour’s deputy leader said: “Boris Johnson must urgently explain why he held a secret meeting with Sue Gray to discuss her report despite claiming her investigation was completely independent.
“Public confidence in the process is already depleted, and people deserve to know the truth. The Sue Gray report must be published in full and with all accompanying evidence.”
Christine Jardine, a Liberal Democrat Treasury spokesperson, said: “Any whiff of a stitch up would make an absolute mockery of the report. This meeting must be explained.”
It has been suggested that the meeting – around one month ago – was to discuss whether up to 300 photos given to the Met probe should be included in Ms Gray’s report.
A No 10 spokesperson said, on Friday: “The prime minister commissioned the investigation led by Sue Gray and has been clear throughout that it should be completely independent.
“As he reiterated again today, the decision on what and when to publish rests entirely with the investigation team and he will respond in Parliament once it concludes.”
Although Downing Street calls the inquiry “independent”, in reality it is an internal process, carried out by a person employed by the government.
The pressure on Mr Johnson has eased, after he escaped further fines for the No 10 parties on top of the one handed down for his cabinet room birthday celebration, in June 2020.
However, the full Gray report could still lift the lid further on what her interim report called the “failures of leadership and judgement”, by revealing the communications leading up to the lockdown-busting events.
The prime minister then faces an inquiry by the Commons’ privileges committee to determine whether he lied to parliament when claimed that no laws had been broken in Downing Street.
Under the ministerial code, any minister who knowingly misleads the House of Commons is expected to resign.