This story has been covered by several sources, but I think this Peston tweet explains it quite succinctly
Just to explain, because the Cabinet Office is paying Boris Johnson's multi-hundred-thousand-pound legal bills, it is technically the client in his defence against the privileges cttee. His lawyers are therefore obliged to submit all material they obtain to the CabOff. Its officials saw diary entries that suggested maybe Covid laws were broken at Chequers events hosted by the then PM. If this was a possible breach of the law, official were obliged under the civil service code to pass info to the police for investigation. It had no choice or discretion in doing this. Its actions were not politically motivated, but were obligatory under the code. It's now for the police to assess whether the law was broken. Johnson's supporters will see this as the "revenge of the blob", but officials - the blob - deny this
twitter.com/Peston/status/1661061779743555598
Barry Humphries..(dame Edna everage) ITV 9pm
Good Morning Bank Holiday Monday 29th May 2023