Some viewers in Britain could receive high-definition digital terrestrial channels by the end of next year under plans outlined by Ofcom. Following a conventional period of consultation, the communications regulator has apparently ignored the expert advice of the Digital Television Group industry association. Ofcom is pushing forward its own plans for a technology upgrade to accelerate the introduction of high-definition on free-to-air digital terrestrial television.

The proposals mean that viewers will require new receivers to access up to four new high-definition channels. The first three channels will be available from 2009 in some regions, starting in the Manchester area.

The plans involve using more efficient technologies: changing the mode of signal modulation, moving to a new transmission standard, and using MPEG-4 video compression.

Ofcom is proposing to clear one of the six multiplexes on which digital channels are broadcast to free up capacity for new services. Multiplex B is currently licensed by Ofcom to BBC Free to View Ltd. It carries BBC Four and CBeebies, BBC Parliament and the Community Channel, the main national radio networks, and four interactive streams. Many of these will need to be squeezed onto Multiplex 1 which is occupied by the BBC.

Once Multiplex B is cleared, the BBC Trust will be allocated one channel, expected to be broadcast in high definition. Three further slots will be awarded to commercial public service broadcasters through a competitive bidding process to be run by Ofcom.

Ed Richards, the chief executive of Ofcom, said in a statement: “This is a once in a lifetime opportunity to upgrade digital terrestrial television. 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.”

Ofcom was asked by the government for advice on how new technologies could be adopted and published a consultation on its proposals in November 2007.

In January, the Digital Television Group pronounced the plans to be “fundamentally flawed”. It suggested that they were likely to compromise the picture quality of existing channels and questioned the assumptions about the timing, technology and transition to new transmission standards.

The Ofcom plans are predicated on the availability of a new transmission standard, DVB-T2, which has yet to be adopted. They also appear to assume that high-definition will be delivered at under 10Mbps, in order to fit the additional channels into the existing capacity.

That could mean using a 720 line progressive format, rather than 1080 interlaced lines. Although it may be argued that most consumers will not be able to tell the difference, the issue of high-definition formats is still a matter of debate among experts.

Some suggest that 1080 progressive is the future. This is already marketed to consumers as Full HD and will become increasingly prevalent with the adoption of Blu-ray Discs, although no broadcasters are currently capable of supporting the format.

There was also criticism that there had been no serious examination of the possible migration to more spectrally efficient single frequency networks. In its extensive document Ofcom makes no mention of the possibility of a single frequency network or SFN.

Ofcom, which generally confines its deliberations to matters of policy and tends to take a consultative, laissez faire approach to its regulatory responsibilities, is being unusually prescriptive and interventionist in its recommendations regarding high-definition terrestrial television.

The issues are complicated by being bound to an already complex plan for switching off analogue signals. They are further confused by proposals from satellite broadcaster Sky to establish a terrestrial pay-television platform, which would also make use of new technology.

While Freeview has been a significant success, following the failure of the OnDigital, latterly ITV Digital, platform that preceded it, it risks being overtaken by advances in television technology.

Consumers are now buying high-definition flat screens that tend to reveal the artifacts produced by the over-compressed signals that are a result of trying to fit more channels into a particular frequency or multiplex.

There is undoubtedly pressure to provide high-definition services on terrestrial television, not least in time for the London Olympics in 2012, by which time most analogue television signals will have been switched off.

In France, plans for mobile and high-definition terrestrial television are well-advanced, partly as a result of a more centralised and interventionist approach to regulation.

Ofcom is making it clear that some of the powers to upgrade digital terrestrial television fall within its remit while others are a matter for the government. Ofcom is seeking an order under the Communications Act 2003 to amend the Broadcasting Act 1996 to facilitate the upgrade.

In the interests of pushing forward a transition to high-definition terrestrial television, Ofcom appears to be setting itself as an arbiter of technical standards, albeit through a consultative process and through reference to unnamed technical experts.

It seems to be something of a snub for the DTG, the industry body which maintains the “D Book” which documents the detailed technical standards for digital terrestrial television in the UK.

It also seems to be something of a rejection of the BBC’s own plans, asserting Ofcom’s authority for regulation.

The BBC Trust gave a guarded welcome to the proposals, which would enable it to launch its own high-definition channel but require it to allocate some existing services to other multiplexes to free up space for other public service broadcasters.

The Trust had been considering a proposal from the BBC in conjunction with ITV, Channel 4 and Five, proposing an alternative way of allocating the available capacity.

“In the light of this, the Trust has decided to suspend our consideration of the BBC Executive’s application pending the completion of Ofcom’s processes,” said Sir Michael Lyons, the chairman of the BBC Trust in a statement.

Whatever happens, there must be some question over the long-term future of the interactive streams that the BBC has maintained on digital terrestrial, used to deliver services such as interactive Wimbledon.

On the other hand, viewers could be watching high-definition channels, although they will need a new receiver. Even if they have a high-definition television with a digital terrestrial tuner, it will not be compatible and they will need a new set-top box to receive the new services.