Ofcom has reiterated its preference for high definition services to use existing capacity on digital terrestrial TV.

In August, the regulator's spectrum policy chief argued against reserving further spectrum for high definition services, a position that is at odd with the HDforAll coalition of broadcasters, manufacturers and some MPs who have said that auctioning off spectrum post-switchover instead of reserving it for HD would render the sustainable provision of high definition services on DTT impossible.

This morning, at a media sector analysts' briefing, Ofcom said that capacity to provide 4 high definition services across the country on DTT could be created without reducing the number of existing standard definition services and without reserving spectrum. It said that post-switchover, a transmission mode change from 16 to 64 QAM - effectively a reversal of the switch to the more robust 16QAM that took place after the collapse of ITV Digital - along with efficiency improvements permitted by statistical multiplexing, and the adoption of DVB-T2, a second generation DTT standard with a new modulation scheme, would create more capacity without the need for new spectrum.

Ofcom added that a change focused on altering technology rather than adding a seventh multiplex would be "quicker and less expensive" and "better for viewers" because a multiplex addition would be "likely to require over 1m households to change aerials."

The regulator will launch a consultation on the HD issue later this year.