The BBC will begin trial broadcasts of high-definition television next year, it announced this week.

Some HDTV sets are already on sale in the UK ahead of the introduction and Sky also plans to launch its own HDTV service in 2006, showing Premiership football.

In the limited technical trials, the BBC plans to simulcast highlights of BBC 1 peak-time schedule in high definition on satellite and cable, as available, from mid-2006.

The BBC also aims to test the format on digital terrestrial TV in London but this will not affect reception of existing Freeview channels.

High definition programmes must also be specially shot. Some BBC programmes, such as Rome and Bleak House, are already made in high definition and the BBC has a target to move all production to high definition by 2010.

HDTV provides a sharper, clearer and more colourful image than the current standard television picture. HDTV sets use a greater number of pixels to display images than on a standard television set. Many HDTV broadcasts will also include a soundtrack that will provide surround sound to viewers using appropriate speakers.

Only viewers with an "HD Ready" television set, a special HD set top box receiver and reception of a high definition service will experience true HD programming.

It is hoped it will be possible to provide a limited number of HD set top box receivers to triallists.

However, it is unlikely that HD receivers will be available commercially until a long-term future is secured for high definition terrestrial broadcasting.

Capacity for high definition broadcasts on terrestrial television (Freeview) will be very limited until digital switchover - between 2008 and 2012.