Alexander Armstrong has said he expects to have his stamina tested during a “demanding” challenge to sing in 24 concerts in 24 hours.
The comedian and television presenter is embarking on the challenge on Thursday.
The fundraiser will see Armstrong perform at locations including a construction site, a football stadium and an airport.
He will also perform a concert with dementia charity Forget-Me-Not Chorus.
Armstrong, 51, who hosts TV quiz show Pointless, will also sing at St Paul’s Cathedral as part of the challenge, which he said will be “heaven”.
“I’m doing a Benjamin Britten piece with them that I know and love, so that will be a real treat,” He added.
“I have never raised my voice in St Paul’s above the sort of reverential whispers that visitors to St Paul’s all adopt.”
He added: “To be singing at the top of my voice is going to be bloody marvellous. I’m going to love that.”
Armstrong, who has released a number of albums including 2015’s A Year Of Songs, said he expects the challenge to be “quite demanding”.
“I think it’s going to draw on stores of stamina, I think,” He also added.
“The actual performing I think is going to be fine. It’s just the idea of being in that zone for that length of time.
“That’s going to be the test.”
Armstrong is a presenter on Classic FM, a classical radio station.
The concerts are raising money for 100 small charities through radio company Global’s Make Some Noise campaign.
Fundraising will be done for food banks, domestic violence helplines, community projects, and employment programs.
Armstrong’s challenge will begin at 12pm on Thursday until 12pm on Friday.