Dominic Cummings will be interviewed as part of an investigation into parties and gatherings at Downing Street during coronavirus restrictions.
Boris Johnson’s former chief adviser confirmed to Sky News that he will be involved in the probe, which is looking at events in Number 10 and other government departments.
And a Cabinet Office source told Sky News: “If we reach the end of the investigation and the inquiry hasn’t spoken to Dominic Cummings, eyebrows would be raised.”
The confirmation that Sue Gray will speak to Mr Cummings comes after he alleged that the prime minister knew in advance about a Downing Street drinks party in May 2020 and agreed that it could go ahead.
These claims have been confirmed to Sky News by a second source, but Number 10 continues to deny that Mr Johnson was told ahead of the event.
The PM maintained this stance on Tuesday, saying in an interview that “nobody told me” the garden party was “against the rules”.