Telecoms giant BT has launched a search to find a new voice for its speaking clock service.

A nationwide competition will be held to mark the 80th anniversary of the service, which receives 12 million calls a year.

The winner will only be the fifth person to give the time "at the third stroke", after people dial 123.

Sara Mendes da Costa has been the voice of the speaking clock since winning the last competition in 2007.

Previous voices have included an actor and a London telephone exchange supervisor.

To celebrate the 80th birthday, BT is 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.

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."

The competition is being run in partnership with BBC TV's The One Show., with the winner announced in November.