High-definition TV sets offer superior pictures and sound quality

After a series of assessments, the body concluded a BBC HDTV channel would offer "high public value" and cause minimal adverse impact on the market.

However, the channel may be delayed on Freeview to save audiences from having to buy two new set-top boxes.

The Trust will now consult the public on the proposals before publishing its final conclusions on 21 November.

An HD service has been proposed for satellite, cable, Freeview and the internet.

Freeview trial

The channel's schedule is expected to draw on programmes from across the BBC's stations and will not be a replication of BBC One.

A trial version is already running on satellite and cable, and should be provided on a continuing basis when a service licence is granted, the trust proposed.

A four-hour service could launch "almost immediately" on Freeview, but the trust said it is to consult the public on this.

Viewers would need to buy a new set-top box to receive the channel - but, because of proposed changes in the way Freeview is broadcast, they may have to upgrade their equipment again when the full, nine-hour service becomes available.

Proposals about the delivery of a full schedule on Freeview will be reviewed early next year.

The service will be assessed during the public consultation period, which has already started and will run until 23 October.

The BBC began trialling HDTV last year with the broadcast of Planet Earth and Bleak House in the format.

A trial of the system using Freeview boxes in November 2006 was deemed "a success" by four major broadcasters.

Channel 4 recently announced that its output would be made available in HD to users with a compatible TV set and Sky HD box.