YOU SWITCH on the television. On the screen is a friendly dealer. The game is blackjack, the American version of pontoon, or vingt- et-un. The dealer asks you how much you want to bet. You say dollars 100. You get a 10 and a nine. She asks if you want to stick or have another card. For the hell of it you decide to take one more.

'You want to draw on 19?', she asks incredulously. 'You're either bold or bad,' she says. She turns over your next card. A two. 'I don't belieeeeve it. I guess it really must be your lucky night. You didn't deserve to get that,' she chides.

This is the reality of interactive television for 65,000 subscribers in London today. The dealer isn't really waiting for you to signal your choice via your remote control. For each turn of the cards there are four choices. It is a little multi-stranded play unfolding. All carefully choreographed. But it is so well put together it is almost impossible to believe that you are not playing the game alone.

The Videoway system, available on the Videotron cable system used to present this game, is technologically unsophisticated compared with systems that are being tried around the world. This just shows how powerful interactive television may become.

Interactive television works by you telling the screen what you want it to do. At the moment, nearly all the truly interactive television is in the laboratory or in small tests. The most eagerly awaited application is called Video-on-Demand (VOD). With this you select a movie from a list. You start the movie running and you can pause when you want. To do this you have to use expensive signalling technology.

Until about 18 months ago, people thought the only way of delivering this service was via cable television systems but telephone companies now have a technology which they claim will deliver video over a standard video line. Any type of programme material can be sent via this system. It could be the latest edition of Star Trek or an instructional programme on Do-it-Yourself keyhole surgery.

Another interactive service the cable companies (and telephone companies) believe will be a real money-spinner is interactive shopping. Again using a remote control, you will be able to browse through a series of choices.

These services depend on two things. First, the system you use has to be able to send a stream of images to your home. This either requires a sophisticated cable system with digital video technology or a telephone system with the technology installed in the local exchange.

The second thing you need, for a real interactive system of even the most basic sort, is to be able to send signals back down the telephone line or cable system. These signals then control the computers that send the information to your home.

At present Videotron offers the only interactive system operational in the UK. It has licensed it Videoway technology to another London cable company, Encom. Other cable companies are also developing systems. BT has a small trial for a telephone-based VOD service.

But the highly interactive world is many years away for most of us. We are unlikely to have fully interactive television in the UK within the next five years and even then only a tiny percentage of the viewing public will sign up. Coronation Street looks safe for another 20 years.