A major upgrade of digital terrestrial television will allow viewers to access more television channels, including programmes broadcast in high definition, the communications watchdog said.

The changes mean that Freeeview viewers should be able to receive up to four new high-definition channels as digital switchover is completed in the UK in 2012, with the first three available as switchover takes place in the Granada and subsequent regions from 2009.

The upgrade can take place without the loss of existing television services currently available to viewers on digital terrestrial television (DTT).

But viewers wishing to access the new services will need to buy equipment that is compatible with the new technologies, such as a new set-top-box, Ofcom added.

Ed Richards, Ofcom chief executive, said: “This is a once in a lifetime opportunity to upgrade digital terrestrial television. It offers benefits for broadcasters – who will be able to launch new services without using any new spectrum – and viewers – who will have access to new channels and services on free to air.”

Ofcom said it is now seeking permission from the government to allow the upgrade.

One of the new slots will be available to the BBC, and it is thought the broadcaster will use this for a BBC high-definition channel.

The other three slots will be awarded to commercial public service broadcasters (ITV, Channel 4, five, S4C) through a competitive bidding process to be run by Ofcom.