The statements, described by one source as “extremely damning”, are expected to form a key part of Ms Gray’s report, which is due to be published within days.

The senior civil servant has also spoken to the Prime Minister, civil servants and political advisers, and accessed security pass logs and even Boris Johnson’s official diary.

Dominic Cummings, Mr Johnson’s former chief aide turned hostile adversary, will be interviewed by Ms Gray on Monday, according to report