The competition has been launched to celebrate the service’s 80th anniversary.
Around 12 million calls are still made to the clock by dialling 123.
The winner will become only the fifth permanent voice of the clock in its history.
The current voice of the clock, Sara Mendes da Costa, who will be one of the judges, said: “I’m so honoured to have been the voice - only the fourth permanent voice in history - and to be part of such an iconic service.
“I’m sad to be at the end of my time as the voice of the BT Speaking Clock, however ten years is not a bad run. And it’ll be great to be on the judging panel to choose the new voice, just as my predecessor Brian Cobby helped choose me.”
The competition to find a new voice will help raise money for the BBC Children in Need appeal. BT will donate 10p to Children in Need from each call to the BT Speaking Clock* from the start of the competition in August until 9 November.
To celebrate the competition and the 80th anniversary, BT are donating the original speaking clock machines from 1936 and 1963 to the British Horological Institute (BHI), where they have been on loan and on display for some years. It will also be donating a digital Mark IV clock, which was recovered from Liverpool. This machine transmitted the voice of Brian Cobby from 1985 – 2001.
David Hay, head of BT Heritage, said: “Eighty years ago BT’s technology first created the Speaking Clock and it remains a much loved part of British life today. Celebrating in this way demonstrates BT’s determination to preserve the heritage of the world’s oldest communications company on behalf of the nation.”
Anyone ten years and over can enter. The competition is being run in partnership with BBC television programme The One Show. Aspiring voice artists should visit the website at: www.bbc.co.uk/theoneshow where they will find full details of how to enter. The website will be open for entries until 10pm on Monday, 29 August 2016.