A fifth high definition digital terrestrial TV channel is expected to launch by April next year.
Ofcom said the extra capacity needed for HD on DTT had been created by reorganising existing TV services and introducing MPEG-4 and DVB-T2.
At the moment the only Freeview HD channels are BBC HD, BBC One HD, ITV1 HD and 4HD.
Public service broadcasters have been invited to apply for the fifth slot.
The closing date for applications 17 October and it is expected that the new channel will launch by 1 April 2012.
In July, the BBC announced plans for a BBC2 HD channel. No proposals have been put to the BBC Trust yet, but they could feature as part of Delivering Quality First.
HD services are currently available to 50% of UK homes with coverage set to rise as digital switchover nears completion in 2012.