Following the announcement earlier this week that the BBC is to go ahead with the conversion of its HD TV trial into a full service, it's emerging that increases in the spectrum available for digital television could bring HD services from the 'big four' terrestrial broadcasters to Freeview as soon as 2009.

On Tuesday the BBC, ITV, Channel 4 and Five announced what they called a 'non-binding memorandum of understanding' to launch HD services between 2009 and 2012. Now broadcast regulator Ofcom has revealed proposals to carry out upgrade work on the digital terrestrial television system, which will be completed by late 2009.

The upgrade, which Ofcom says could more than double the capacity available on the Freeview platform, will allow new services, not all of them HD. But viewers wanting to see Freeview HD will need to buy a new set-top box as well as an HD-compatible TV.