Some media have reported that the opening of a police investigation into the allegations would delay a report by civil servant Sue Gray, suggesting a delay might buy time for the prime minister.

The spokesman said Gray's team was discussing with the police whether she could still release her report in full after parts of it had been passed to them for their investigation, adding Johnson's office was not involved in those discussions.

"There are discussions still ongoing between the investigations' team and the police," he told reporters.

"That still needs to be worked through both in relation to what may or may not be published and the ongoing work of both the police and the investigation."

"We are not seeking to block that (the publication of the report) in any way," he added.

(Reporting by Kylie MacLellan, writing by Elizabeth Piper; editing by Michael Holden)