The UK's main terrestrial broadcasters have agreed a joint blueprint for the roll-out of high definition TV services on Freeview.
The BBC, ITV, Channel 4 and Channel Five have signed a "non-binding memorandum of understanding" that could see the introduction of HD channels on Freeview by late 2009.
The landmark agreement represents a major volte face by the broadcasters.
They had maintained there would not be enough capacity on Freeview for HD channels unless media watchdog Ofcom set aside capacity freed up by digital switchover.
The broadcasters are part of lobby group HD for All, which has been pushing for capacity to be set aside for HD channels rather than auctioned off - as Ofcom would prefer.
As recently as May, ITV's executive chairman, Michael Grade, maintained that launching HD channels using existing spectrum would present "insurmountable practical, legal and financial hurdles".
Today's agreement between the broadcasters comes ahead of an announcement by Ofcom tomorrow morning of a consultation into the future of digital terrestrial television.
The first services to be launched will be BBC HD, which was approved by the BBC Trust yesterday, ITV HD and Channel 4 HD.
Channel Five's service will follow as soon as capacity is available and by 2012 at the latest.
The agreement involves the use of new technologies to increase capacity on Freeview and a rearrangement of some of the channels carried on Freeview,
One of the BBC's two Freeview multiplexes will need to be set aside to make the launch of the HD channels possible.
The proposed agreement will require approval from the BBC Trust, as well as regulatory approval from Ofcom.
Sky is already a major HD player, having launched its own service in May 2006. It has so far signed up around 360,000 customers.
Channel 4 plans to launch an HD service on Sky in December, while the BBC has been trialling an HD channel on digital satellite and cable TV.

THIS ARTICLE IS ABOUT HD JOINING FREE-VIEW CHANNELS. THERE HAS BEEN AN ISSUE THAT THERE ARE NOT ENOUGH CHANNELS TO PROVIDE THE HD CHANNELS UNLESS OFCOM SET ASIDE SOME CHANNELS. THE CHANNELS WILL NEED PERMISSION WITH THE BBC THEY NEED IT FROM THE BBC TRUST AS WELL AS OFCOM.