Ofcom chief Ed Richards claims Freeview could add up to four high definition channels by 2009 if broadcasters accept its plan to rearrange the Freeview multiplexes.

Speaking to the Broadcasting Press Guild, Mr Richards promised to publish details of Ofcom's controversial plan "in the autumn".

Freeview's six multiplexes are not being used to their highest efficiency, and up to four hi-def channels could be accommodated by reallocating the bandwidth and using new compression technologies such as MPEG-4, he added.

"We are in favour of high definition TV on Freeview," he said. "It provides a growth path for the platform and ensures it will be competitive in the future."

He said "one or two" of the public service broadcasters were now in favour of Ofcom's plan.

Mr Richards admitted the viability of Ofcom's proposal has only been "technically proven", but said it would cost much less to build using existing transmitters than a seventh mulitplex, as proposed by HDforAll.

Adding a seventh multiplex would also prevent the launch of hi-def on Freeview until after analogue switch-off in 2012, he warned. On the existing muxes they can be launched by 2009 or 2010.