Which? magazine says early buyers of set-top boxes and expensive new televisions may lose out in the same way as owners of betamax videos and the squariel satellite receiver before them.

...if you have the right little black box...

It says that it will take years for the television revolution to settle down into a market which gives the consumer the best value for money.

Until then buyers may want to hang on to their cash.

Digital television is being launched in the UK later this year when three competing services, the first operated by BskyB, get off the ground.

Commercial televisions stations and the BBC are also launching digital television services.

It will be the biggest change to broadcasting since the switch from black and white to colour.

Digital television uses new technology to compress broadcasting signals which means much more information can be sent into the living room at the same time, potentially creating up to 200 television channels.

...so that you can surf through the airwaves...

Media organisations say this will bring more programme choice, expand pay tv, launch interactive services such as shopping and education, and eventually lead to a merger between the Internet and broadcasting.

Subscribers to digital television will need a set-top box, rather like a satellite decoder, to receive signals.

But according to the Which? report, this technology will be expensive and may become obsolete within a matter of years.

It says BskyB's proposed £200 decoders could later be replaced by boxes which will be able to receive both digital satellite and terrestial signals.

Eventually the box will be built into the television itself, the report continues.

...to find the service which you want.

Andrew McIlwraith, senior editor of Which? magazine, said: "It might be tempting to be at the forefront of new technology, but it's probably best to wait in the case of digital television.

"Upgrading TV equipment may be inconvenient and expensive and if you leap too soon, it could quickly become redundant.

"There does not even appear to be any guarantee that going digital will mean better picture quality and an improved range of programmes."

Digital television has already started on the continent but it is too early to tell how successful it has been.

In Germany, two media giants have finally reached an agreement on what technology to use as the standard while in France broadcasters say their services are heading for profit next year.