Most digital television channels - but not all - are pay services. Among the additional free channels are three from the BBC: News 24, BBC Choice and BBC Four.

All have proved controversial with the BBC's commercial rivals, who claim the BBC's offerings (advertising and subscription-free) are driving their equivalents out of business.

A plan to revamp Choice and Knowledge as BBC Three (aimed at younger audiences) and BBC Four (a kind of television equivalent of Radios 3 and 4), with programmes for children during the day, proved especially controversial.

Sports-mad men are prime interactive TV users, research says

Operators of commercial children's channels like Disney, Nickelodeon and Fox Kids have protested loudly at what they see as unjustified licence fee-subsidised competition.

The government has approved BBC Four, which has now launched, but is still considering BBC Three.

The BBC argues there is a role for commercial-free children's TV, and that its plans overall make sense in a world of ever-increasing numbers of channels, each carrying a distinctive kind of programming and aimed at a particular kind of audience.

A BBC confined to just two mixed channels would be condemned to long-term decline - a BBC with a range of "genre-based" channels stands a chance of retaining its audience and justifying a continuing licence fee.

There remain two big unanswered questions about digital TV in Britain. The first is how quickly it will become universal.

Chris Smith: Aims to end analogue TV by 2010

Although a third of the country now has at least one digital set, two-thirds do not.

These are people who have remained steadfastly indifferent to the lure of multichannel television even after more than a decade of Sky TV.

If they have survived this long with just four or five channels, they may be content to go on with just four or five for years to come.

This is bad news for the government, which wants to turn off the existing terrestrial TV transmitters which broadcast old-style 625-line PAL television by 2010 at the latest, and if possible 2006.

Switched off

The aim is to auction off the frequencies to other users like mobile phones companies.

This analogue-digital switch-over presents a delicate political problem, however.

Former culture secretary Chris Smith promised that analogue switch-off would not happen until 95% of the population has a digital set.

To get to that point may require some form of subsidy from the public purse.

Even then, the remaining 5% without a digital set are likely to include the oldest, poorest and most disadvantaged in society - and no government could contemplate depriving them of their televisions.

Interactive appeal?

And even when every home has at least one digital set there will still be tens of millions of second, third and fourth sets in bedrooms and kitchens across the nation that will be rendered obsolete the day analogue transmitters are switched off.

The other unanswered question is how far consumers will take to the possibilities of interactive television?

Will the TV in the corner of the living room ever become a "lean forward" device on which we routinely send and receive e-mails, do our weekly shop or surf pages of information as we do on the net?

Early indications are mixed.

Slow and clunky

Sky's Open service has 37 main content providers, including retail chains like Woolworths and banks like HSBC, and 84 smaller ones.

The company says two-thirds of digital satellite subscribers have used it - but by the end of last year those 3.5 million homes had between them placed only 655,000 orders, and Open's revenue in the second half of 2000 was just £36m.

Research among digital subscribers suggests many find interactive services slow and clunky, with poorly designed sites and a disappointing range of products on offer compared with shopping online via the internet.

Families report rows breaking out between those who want to use the household's only digital set for home shopping or sending e-mails and those who want to watch digital TV channels.

TV betting success

Around half of digital TV subscribers are largely indifferent to the interactive services, and TV remains far less important as a way of accessing online services than the PC.

On the other hand some interactive services have proved wildly successful, notably television betting - by the end of last year Sky had 15,000 TV betting accounts and revenues from screen betting of £33m in the previous six months.

Researchers have identified some groups - especially sports-mad men - for whom interactive services are highly important and attractive.

The digital television has the potential to change beyond recognition the role of the box in the corner of the room, forcing us all to rethink our relationship with a device which for most of us dominates our leisure time and our leisure spending.

Whether it will or not we still do not know.