Viewers will be able to watch high definition TV on Freeview from 2009, broadcast watchdog Ofcom has confirmed.
Ofcom says new technologies as well as the effects of digital switchover will enable more channels, including HD services, to be broadcast.
But viewers who want to watch the new services, which will first appear in the north-west of England, will need an HD-ready TV and a new set-top box.
Up to four free HD channels will be broadcast, including the BBC's service.
ITV, Channel 4, Five and Welsh network S4C will be invited to bid for three slots in which they can broadcast high definition TV, or other new services.
Ofcom says the new services should add to the "range and diversity" of TV in the UK, and contribute to public service broadcasting.
Viewers will have to wait until analogue TV is switched off in their area before they can see the HD channels. The last regions to change to all-digital signals, in 2012, will be London, the north-east of England and Northern Ireland.
At present, viewers can only watch HD services via satellite or cable, with most paying a subscription.
Free satellite TV service Freesat, which will include HD services from the BBC and ITV, will launch later this year.
Ofcom chief executive Ed Richards called the change a "once in a lifetime opportunity".
"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," he said.
Ofcom will change the way digital terrestrial television channels are arranged to clear the way for the new services.
They are arranged in six "multiplexes" - bundles of channels, each operated by different companies.
One of the multiplexes, currently run by the BBC, will be have its channels moved elsewhere to create space for high definition channels and other new services.
Each high definition channel takes up four to five times the space of a standard service.
New technology means each multiplex will be able to carry more channels, and once analogue TV is switched off, the quality of the signals will improve.