The developments leave Mr Johnson in limbo, unsure what will be contained in Ms Gray’s report or when it will be released, as Tory MPs weigh up whether to oust him.

It came on a day of finger-pointing and confusion about who is to blame for the delay in Ms Gray’s report.

On Friday morning, the Metropolitan Police had been accused of a “disproportionate” approach by insisting Ms Gray only reveals “minimal” information about the “partygate” events it is now probing.

Legal experts and MPs had argued that there was no way any prosecutions launched from the probe could be prejudiced because they involved fines overseen by judges, not a jury.

Police ask for ‘minimal reference’ to relevant events

On Friday night, a statement issued in the name of Commander Catherine Roper, who is overseeing the investigation, doubled down on the position, arguing it was “in order to protect the integrity of the police investigation”.

But the statement also revealed that relevant “material” had been delivered from the Cabinet Office, under which Ms Gray is conducting her probe, to Scotland Yard on Friday.

One government source told The Telegraph the material could include hard evidence such as witness statements, photographs or text messages about the events being probed.

Part of the statement read: “In order to protect the integrity of the police investigation, as is appropriate in any case, and to be as fair as possible to those who are subject to it,  the Met has asked for minimal reference to be made in the Cabinet Office report to the relevant events.

“This will only be necessary until these matters are concluded, and is to give detectives the most reliable picture of what happened at these events. We intend to complete our investigations promptly, fairly and proportionately.

“We have not delayed this report and the timing of its release is a matter for the Cabinet Office inquiry team.”

The statement also made clear the next steps for those accused of rule-breaking at the alleged events. The Telegraph understands eight gatherings are being investigated.

It read: “Individuals who are identified as having potentially breached these regulations will normally be contacted in writing, and invited to explain their actions including whether they feel they had a reasonable excuse.”

“Following this process, and where there is sufficient evidence that individuals have breached the regulations without reasonable excuse, officers will decide if enforcement action is appropriate.

“If the decision is to take enforcement action then a report will be sent to the ACRO Criminal Records Office which will issue the fixed penalty notice. Recipients can pay the fixed penalty and the matter will be considered closed.”