The pair are understood to have held at least one meeting to give an update on the document’s progress as it was being drafted, but a Whitehall source said its contents were never discussed.
Such meetings would not have been seen as unusual, the source said, in order to assess the stage of the report.
It comes as the Cabinet Office contacts some 30 people, including Johnson, to warn them about the document’s contents before publication.
Angela Rayner, deputy leader of the Labor Party, asked the prime minister to “urgently explain” why the “secret meeting” had taken place.
He said that public confidence in the process had already been “exhausted” and that people “deserved to know the truth.”
Downing Street insisted that the prime minister had been “clear throughout” that the report should be “completely independent”.
Most of the Cabinet Office letters are believed to have been sent on Thursday, when the Metropolitan Police concluded their investigation into lockdown breaches in Downing Street and across Whitehall.
Mr. Johnson will be among those contacted, but No. 10 did not have an update on whether he had received a letter on Friday night.
Ms Rayner said: “Boris Johnson urgently needs to explain why he held a secret meeting with Sue Gray to discuss her report despite claiming her investigation was completely independent.
“Public trust in the process is already exhausted and people deserve to know the truth.
“This is a Prime Minister unable to take responsibility for the rotten culture he has created in Downing Street or to do things decently.
“Sue Gray’s report must be published in its entirety and with all accompanying evidence.”
Adam Wagner, a human rights lawyer who has specialized in breaking lockdown rules, said the document was “not an independent report” and “never has been.”
It’s an internal report. This is not a judgment on Sue Gray, this is a statement of fact: She is an employee investigating her direct managers,” she tweeted.
A No 10 spokesman said: “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 answer in Parliament once it is concluded.”
Not all persons contacted by the Cabinet Office will necessarily be named or otherwise identified in the report; it may simply be that their actions are referenced because they are pertinent to the narrative of a particular event.
It is understood that the researchers do not include the full details of the document’s content in the letters, but rather provide a “gist” of the relevant sections to those who are approached.
Sources close to the investigation expect the report to be released early next week.
Johnson refused to apologize again for breaking the rules in number 10 during a visit to Hilltop Honey’s factory in Newtown in Powys, Wales, on Friday.
Asked if Downing Street would block names from appearing in the report, he said: “That will be entirely up to Sue Gray and I’ll be keen to see what she has to say, and my fingers are crossed that it will be very soon next week.”
I think without the police providing an explanation for that, it’s very difficult for us to understand why they came to the conclusions that they did.
There were calls for Scotland Yard to explain how Mr Johnson received only a fine, for his 56th birthday gathering in June 2020 when indoor mixing was banned.
The former director of public prosecutions, Lord Ken Macdonald, warned that “it is very difficult for us to unravel exactly how the police investigation has proceeded and how fair it has been”.
He told BBC Radio 4’s Today programme: “I think without the police providing an explanation for that, it is very difficult for us to understand why they came to the conclusions that they did.”
The bench mate said it was not known why the prime minister was fined for his presence at what was considered one of the less serious events, but not at others.
Nor has it been explained why Cabinet Secretary Simon Case, who had to refrain from conducting the civil service investigation after reports of a Cabinet Office Christmas party surfaced, has not been fined.
The Met refused to identify anyone in its £460,000 investigation.
A team of 12 detectives examined 345 documents, including emails, door searches, diary entries, witness statements and 204 questionnaires.
They also examined 510 photographs and CCTV images.
Johnson, his wife Carrie Johnson and Foreign Minister Rishi Sunak were fined for the birthday gathering.
But police have told both Johnsons they will face no further action, according to Downing Street, and Sunak has not received an additional fine.
The Met said 28 people had received between two and five tickets.