Five TV transmitters covering some of the UK's most heavily populated urban areas, including London, Birmingham, the north-west and the north-east, are set to receive the service between December this year and June 2010.
Each one will have to be upgraded and the plan is to do so in time to broadcast the football World Cup in South Africa next summer.
Danielle Nagler, head of BBC HD, says: "We could see an earlier provision for Freeview HD in the UK. Technically, in December 2009 there's a switchover.
"If the plans for new transmitters go ahead, 45-50 per cent of the country will have access to the technology. The World Cup in June 2010 will be a strong marketing target point."
However, Nagler adds that the 2010 date originally set for making 100 per cent of BBC1 and BBC2 peak-time content in HD "isn't going to happen", partly because the costs of producing TV programmes in HD haven't fallen as fast as had been hoped.
New set-top boxes required
Of course those wanting to watch Freeview HD will need to buy a new set-top box. Given that the final technical specs for Freeview HD set-top boxes have only just been agreed, so theoretically some boxes could be on sale by Christmas this year, it's unlikely Freeview HD PVRs (personal video recorders) will be available until part way through 2010.
However, existing Freeview set-top box owners will also be affected, with the required channel reorganisation to make way for HD requiring existing channels to change the frequency on which they broadcast.
This means up to 18 million Freeview users in the affected areas will have to manually retune their boxes to find the channels on their new frequencies.
While this shouldn't be too taxing – it's a simple operation with the menus, and many boxes will prompt users to retune for new channels anyway – there's no doubt a potential problem for less tech-savvy consumers.
Broadcasters have said that a plan to communicate the changes to viewers has not yet been worked out, although onscreen warnings, leaflets and extra information on Freeview's website is expected.
Around 17.7m UK homes had access to digital TV via Freeview by the end of last year, according to the latest figures from Ofcom.