The main terrestrial television broadcasters in Britain, the BBC, ITV, Channel 4 and Five, have agreed a joint approach to deliver high-definition television channels on Freeview. The broadcasters appear to have accepted the view that they can do so within their existing broadcast capacity. They had been arguing the need for more spectrum once existing analogue services are switched off.

The British public service broadcasters have signed a non-binding memorandum of understanding that could see the introduction of high-definition channels on the Freeview digital terrestrial television platform from the end of 2009.

It represents an apparent climb-down by the British broadcasters which had been lobbying for additional capacity to be set aside for high-definition channels, rather than being auctioned when the existing analogue channels are turned off.

Instead it seems they will use capacity that was allocated to the BBC following the collapse of ITV Digital prior to the launch of Freeview. The announcement of the agreement came the day before the communications regulator Ofcom launched one of its customary consultations on the matter.

The broadcasters have agreed a rearrangement of some of the channels carried on Freeview, setting aside one of the two BBC multiplexes for the carriage of not only the BBC HD service, but also high-definition services from ITV, Channel 4 and ultimately Five.

In a brief joint statement the broadcasters said the agreement “follows discussions with Ofcom and Government to launch the new services consumers want, in particular free-to-air High Definition.”

The first services could be available from late 2009 or early 2010, with Five following as soon as capacity is available, by 2012 at the latest.

The plans will require new technologies to make more efficient use of existing capacity, as well as approval from the regulator and relevant broadcaster boards. A variation of the relevant BBC multiplex licence to carry high-definition services will be subject to approval from Ofcom as well as the BBC Trust.

The BBC uses two multiplexes on digital terrestrial television, known as Mux 1 and Mux B. The first of these currently carries BBC One, BBC Two, BBC Three and CBBC, BBC News 24 and the BBCi digital text service. Mux B currently carries BBC Four and CBeebies, BBC Parliament, a number of network radio services, as well as interactive streams.

The high-definition plans put in question the future of some of the interactive services. At least two interactive channels are now only used on an occasional basis.

The announcement by the broadcasters pre-empted proposals from Ofcom for an upgrade of the digital terrestrial television platform. Although Ofcom tends to prefer a laissez-faire non-interventionist approach, it seems that the BBC may have come under some pressure to release some of its valuable multiplex capacity to competing broadcasters.

New transmission standards will enable more efficient use of existing capacity. These include a proposed modulation scheme mode change, using a new transmission standard known as DVB-T2 which has yet to be finalised, and the use of MPEG-4 encoding. Taken together, Ofcom says these could in time more than double the channel capacity available.

It is suggested that using the new standards, a single multiplex could carry four high-definition services. Some industry observers have questioned this assumption, noting that the current standard definition channels are already over compressed, resulting in inferior image quality. Viewers would also require a new compatible set-top box or digital television to view these services.

Ed Richards, the chief executive of Ofcom, said: “Our proposals to upgrade digital terrestrial television represent a major opportunity to build on its success with wider, richer and more varied television services, including the potential for HDTV to be made available to millions of people free to air.”

Earlier in the week, the BBC Trust approved proposals for a mixed-genre high-definition television channel, BBC HD, to be available on satellite, cable, and in due course on digital terrestrial and the internet. The channel will be part of the line up on Freesat, a joint venture free-to-air satellite service from the BBC and ITV that is due for launch in the spring of 2008.