In the autumn, Bell Cablemedia, Nynex CableComms and TeleWest Communications will begin a joint research project to use cable’s fibre-optic lines to offer their viewers a library of television programmes from which to choose, which can be started and stopped whenever the viewer wants.

Rather than watching what the broadcasters have scheduled, viewers would pay to watch television programmes or feature films, selecting from a huge range of titles which could be called up from a central computer server.

Already British Telecom and Cambridge Cable and Acorn Computers have been testing similar on-line projects, with all competitors hoping to cash in on the introduction of computer-based services, operated through the approachable shop-window of the television screen.

There are similar schemes under research in the United States, and in the Netherlands, Philips is working on a video on demand system based on its CD-i technology.

Along with pay-television and video, the facilities will include home banking, shopping and business information.

For education, the service could mean that an archive of schools television programmes or videos could be made available at the push of a button, or other multimedia material, such as CD-Roms, could be accessed from the classroom.

In the joint cable venture, 2,000 homes will be connected in field tests, in franchises owned by the three participating companies, spread throughout the country.

If the system is proved technically feasible, then the next stage of this challenge to television as we know it will be to decide on the type of programming to offer and the crucial question of price.