Rishi Sunak’s administration refused a demand from the UK’s Covid-19 inquiry to hand over former prime minister Boris Johnson’s WhatsApp messages and pandemic diaries, setting up a legal battle that risks amplifying accusations of a cover-up.

The Cabinet Office on Thursday said it’s filing for a judicial review into the request for the unredacted documents by Heather Hallett, the retired judge appointed by the government itself to lead the inquiry. A spokesperson for the probe said in an email that a preliminary hearing is scheduled for Tuesday.

The approach will open Sunak up to further accusations that he is attempting to cover up sensitive information, given that the requested documents are also likely to include his own correspondence with Johnson, as he was Chancellor of the Exchequer at the time.