Labour leader Keir Starmer has tested positive for coronavirus and will miss Prime Minister's Questions today.
Deputy Angela Rayner will take his place for the first PMQs clash of the year, a party spokesman said.
It is understood that Mr Starmer is feeling well. He has been doing daily lateral flow tests and today's came back positive.
It is the sixth time Mr Starmer has had to self-isolate.
He was forced to miss Budget Day in October after testing positive for the virus.
Shadow Chancellor Rachel Reeves stepped in to respond to Rishi Sunak's Budget speech at the last moment, while Ed Miliband, who was then the Shadow Business Secretary, took PMQs.
Mr Starmer was also told to isolate four times in 2020 and 2021 after being a contact of a positive case.
It comes a day after he gave a major speech in Birmingham on his new contract with the British people, based on "security, prosperity and respect".
In the audience were a small group of city Labour MPs including Jess Phillips, Khalid Mahmood, Jack Dromey, Stephen McCabe and Preet Gill, together with journalists and party advisers.
The 20-strong crowd also included Birmingham City Council leader Cllr Ian Ward, and the West Midlands regional police and crime commissioner Simon Foster.
Ms Phillips, Ms Gill and Cllr Ward also later joined the Labour leader on a tour of a green energy and decarbonisation research site.
Mr Starmer's positive test will come as a blow to the Labour leader on a busy day in Westminster as MPs return to Parliament after the festive break.
Prime Minister's Questions will be held at the later time of 3pm as the House of Commons on sits from 2.30pm today.
Boris Johnson will then give a statement to MPs after addressing his Cabinet on soaring Omicron cases.
The PM is expected to maintain Plan B measures for England, as he seeks to "ride out the Omicron wave" without the need for further restrictions.
There are expected to be some changes to testing rules, including scrapping the need for a confirmatory PCR test after a positive lateral flow result.
