It means the two broadcasters will join the BBC in being able to broadcast HD services on Freeview. It's believed a fourth HD service could be launched on Freeview by 2010.
The new Freeview HD services will be available on a region by region basis as the UK switches over to digital TV. Viewers in the Granada region should be able to watch HD programmes from late 2009, followed by Wales, Scotland and the West Country in 2010.
Viewers in Central, Yorkshire, Anglia and Meridian will be able to view HD programmes on Freeview in 2011, while London, Tyne Tees and Ulster will be the last to get them in 2012.
Viewers will need an HD-ready or Full HD TV and a new Freeview HD set-top box to watch the new services, but they'll be received via a roof-top aerial rather than a satellite dish as is the case with rivals Sky and Freesat.
Ofcom chief executive Ed Richards says: "This is a major step in the development of digital terrestrial television. It will enable viewers to watch some of the very best programmes free-to-air in high-definition through their televison aerials."
Rival HD service Freesat, which is available now, claims its satellite service can reach 98 per cent of UK homes now whereas Freeview HD won't be available in all regions until 2012, and current Freeview coverage is only 73 per cent of UK households.
"In order to view HD channels on Freeview, consumers will need to replace their existing Freeview receiving equipment," says Freesat.
