Tess Alps, the chief executive of the TV marketing body Thinkbox, said: "More HD capacity generally is great, whatever the platform, and we welcome this expansion with open arms. To be globally competitive, the UK needs to produce more HD content."
She added that research shows there is around 10 per cent more engagement with TV advertising shown in HD: "Advertisers should be enthusiastic about the opportunities offered by HD, and the other hugely inspiring technological advances in TV."
Ofcom said the upgrade of digital terrestrial television, which will be delivered via the use of new technology and by using spare multiplex capacity, would create more consumer choice and generate up to £6 billion in advertising and other revenues over 25 years.
The changes will create four HDTV channels on Freeview by the time the digital switchover is completed in 2012, with three of them launching by 2009. The regulator will invite proposals from the major public service broadcasters, BBC, ITV, Channel 4 and five, on how the upgraded capacity should be filled, and they are expected to compete for the HD capacity.
Ofcom's plans will make HDTV free to air for the first time. Sky has its own HDTV service, needing a Sky HD box and a subscription, while other broadcasters, including the BBC, offer HD via satellite.
Ed Richards, the chief executive of Ofcom, said: "Our proposals to upgrade digital terrestrial television represent an opportunity to build on its success with wider, richer and more varied TV services."