The development leaves Mr Johnson in limbo, unsure what will be contained in Mrs Gray’s report or when it will be released, as Tory MPs are considering whether to oust him.
It came on a day of clues and confusion as to who is to blame for the delay in Mrs Gray’s report.
On Friday morning, the Metropolitan Police had been accused of a “disproportionate” approach by insisting that Ms. Gray reveal only “minimal” information about the “partygate” events it is now investigating.
Legal experts and MPs had argued that there was no way any prosecution initiated from the investigation could be harmed because the fines involved were monitored by judges, not a jury.
Police are asking for ‘minimal reference’ to relevant events
Friday night, a statement issued in the name of Commander Catherine Roper, who oversees the investigation, doubled the position, claiming it was “to protect the integrity of the police investigation.”
But the statement also revealed that relevant “material” had been provided from the Cabinet Office, under which Mrs Gray is conducting her inquiry, to Scotland Yard on Friday.
A government source told The Telegraph that the material could include hard evidence such as testimony, photographs or text messages about the events being investigated.
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 requested minimal referral. the Cabinet Office report to the relevant events.
“This will only be necessary until these cases are completed, and that is to give the detectives the most reliable picture of what happened at these events. We intend to complete our investigations quickly, fairly and proportionately.
“We have not delayed this report and the timing of its release is a matter for the Cabinet Office’s investigation team.”
The statement also made clear the next steps for those accused of breaking rules at the alleged events. The Telegraph understands that eight assemblies are being investigated.
It read: “Persons identified as potentially having violated these rules will normally be contacted in writing and asked to explain their actions, including whether they feel they had a reasonable excuse.”
“After this process, and where there is sufficient evidence that individuals have violated the rules without reasonable excuse, officers will decide whether enforcement measures are appropriate.
“If the decision is to take enforcement action, a report will be sent to the ACRO Criminal Records Office, which will issue the fixed fine. Beneficiaries can pay the fixed fine and the case will be considered closed.”