The new digital services are important to director-general Greg Dyke

The publicity campaign, which will also include off-air advertising in posters, newspapers and magazines, is said to be the biggest the BBC has ever mounted.

It's motivated, of course, by self-interest - there's no point in launching these new services if no-one watches or listens - but it's also something the government insisted on when it gave permission for the launch of eight new services.

Technophobia

The government perhaps hoped for a generic campaign trumpeting the virtues of digital broadcasting.

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In its advertising the BBC has opted mainly to promote individual services, on the grounds that most people aren't interested in the technology itself - indeed, to many the word "digital" simply provokes acute technophobia - but are potentially interested in the programmes or channels it can deliver.

The publicity campaign comes at an interesting moment. The number of digital homes has reached nearly nine million - around a third of the country.

But the rapid rate of growth of the last three years is slowing down significantly.

The Henley Centre reckons digital TV penetration could plateau at around 50 per cent.

That's a long way from the government's target of near-universal access to digital by 2010.

'Refuseniks'

Research suggests that the two-thirds of households who don't yet have digital include a high proportion of "digital refuseniks" - people who say they simply don't want it: they think they can't afford it or they're perfectly happy with just five channels.

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Hence the importance of initiatives like the BBC's, which apart from anything else will emphasise that digital television doesn't have to mean pay television.

But promoting free-to-view digital will be little use until it's possible to buy an affordable digital receiver without coughing up for a subscription.

Walk into Dixons and you'll be offered ITV Digital and Sky receivers, but only as part of a pay-TV deal.

Sky used to give people who just wanted the free channels a free box, provided they connected it to a phone line and paid a �100 installation fee. Since New Year's Eve it's started charging �220 for the box.

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ITV Digital boxes can be bought without a subscription in some independent retailers - but they too cost more than �200.

And integrated digital television sets, with the DVB kite mark and all the digital gubbins built in, can set you back at least �700 or �800.

Cheap box

Meanwhile industry-wide talks on developing a cheap free-to-view set top box, selling for around �100, seem to have made little progress.

The BBC, ITV, Channels 4 and 5, retailers and manufacturers and perhaps Sky are all potential partners in such a venture.

But there are difficult questions still to resolve - not least about who pays what, and about just how big the potential market for free digital services really is.

So for now, although in theory it's true that digital television doesn't equal pay-TV, in practice it might as well be the case.

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A version of this article appears in the BBC magazine Ariel.