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On my last visit to Kingswood Warren, just before the ³ÉÈË¿ìÊÖ Research and Development team packed their bags and moved to Manchester and London, I spotted an enormous, bulkyÌýold television set tucked away in a corner of the neo-gothic house.

Forlorn and covered in dust, this was part of television history. It was the set used for early experiments in HDTV, which Kingswood began nearly thirty years ago. Graham Thomas, who showed me around, explained it took six men with two poles to lift. Which presumably explains why it's still sat there, silently watching its flat screen progeny.

High definition, as the name implies, allows you to see images in greater detail than standard definition sets. Thanks to those experiments we can now watch Barcelona play Madrid off the pitch, sink into the sofa to watch the latest Blu-Ray release or play immersive video games, all in up to five times more detail.

The first HD sets which came to market and which are often labelled 'HD Ready' or 'HD Ready720' have twice as many pixels (720 lines of 1080 pixels) as standard definition sets. Most larger screens sold today are branded 'Full HD' or 'HD Ready1080' and have five times the number (1080 lines of 1920 pixels).

You're likely to pick up a HD Ready720 set for less money and they’re worth considering if you only want a smaller screen size, where the advantage of having more pixels may be lost.

If you're buying a larger set and want to enjoy movies at their most impressive, then investing in Full HD means more pixels - and smaller pixels, at that - delivering better image quality.

Where you see 1080p or 1080i, the letters refers to the way the image is built on the screen, whether it's an 'interlaced' or 'progressive' system.

When images change on screen, the whole picture doesn't change instantaneously. In interlaced systems, odd numbered lines change first, then even numbers, so it takes two scans to change the picture. It happens in a millisecond, faster than can normally be detected by the human eye. With 'progressive' systems the picture change is achieved in one scan which sweeps from top to bottom.

Interlaced scan is usally better for watching sport, as it can display quick movements more easily. But for something slightly more sedate, such as a drama, progressive scan will deliver a clearer picture.

But don't just rely on the numbers. A 720 line set with excellent picture processing could out-perform a 1080 line TV with poor picture processing. So when buying a set check the screen quality. One tip is to ask retailers to play a movie by carrying the same player to different sets. You might not be the most popular person on a busy Saturday morning but it will give you a chance compare like with like.

To see those pictures you'll need more than a HD television, you'll also need some kind of HD video source. Unless the set has a built in HD tuner, you'll need to buy additional equipment or subscribe to a service provider.

The basic choice is between a subscription or non-subscription route. You can buy Freesat or FreeView HD kit outright or take out a subscription package with Sky or Virgin Media. Obviously, there are different costs and it all depends on what you want to watch.

Although not all TV programmes are available in HD, there's plenty of content to enjoy, like a wide choice of Blu-ray movies and video games.

The ³ÉÈË¿ìÊÖ have two HD channels: The ³ÉÈË¿ìÊÖ HD channel, which showcases the best HD programmes from across all ³ÉÈË¿ìÊÖ channels, from Wimbledon to Wonders of the Universe and the more recent ³ÉÈË¿ìÊÖ One HD channel which simulcasts a network version of the ³ÉÈË¿ìÊÖ One schedule, showing the majority of peak time programmes in HD.

Broadcasters are still learning how exploit the full creative potential of HD. Danielle Nagler, Head of ³ÉÈË¿ìÊÖ HD, says one of the biggest challenges has been encouraging producers not simply to make the same programme in HD, but to use it to make even better programmes.

In drama, this means being more filmic, with more close-ups. In natural history, perhaps including spectacular detailed helicopter shots. But there's a downside - Danielle says, 'HD can break the illusion, so it's vital to remember scratches or screws on sets become visible and artificial flowers or even some wigs that work in SD may not be convincing in HD'.

Danielle adds that HD is more precise and less forgiving. and imperfect technique can impinge on the whole work. 'In many ways HD has reminded people of the craft of filming'.

It might not surprise you to learn that the advent of HD transmission meant the installation of two and a half kilometres of cable and a hundred and eighty five separate pieces of equipment in the ³ÉÈË¿ìÊÖ apparatus room. It's worth watching this video Danielle made when ³ÉÈË¿ìÊÖ One HD launched explaining just how the channel gets to air. /bbchd/faqs.shtml

Meanwhile one former Tomorrow's World producer feels vindicated. Saul Nasse remembers filming a piece about widescreen television with Kate Bellingham at the French Open in 1991, where both HD-MAC (the high definition standard) and D-MAC (the widescreen standard) were being used.

'We'd been talking about high def on TW for years,' he says, 'and even though the pictures were brilliant, we made the point in my story that viewers were all likely to see widescreen standard definition sets in their homes long before high definition, which would probably have to wait for fully digital television. We weren't always right with our predictions on Tomorrow's World, but this time we were spot on!'