The internet reaches about 60% of the population, and many of those offline are perfectly happy to stay there. This represents a problem for electronic government, particularly as non-users are disproportionately elderly and poor: those who make the heaviest use of government services.

So digital television looks like an attractive alternative: 47% of homes had access in the third quarter of last year, according to the regulator Ofcom, and numbers are rising fast. Sky has 7.2m satellite subscribers, and it aims to reach 8m by 2005. The subscription-free Freeview terrestrial service has gone from 800,000 using the ITV Digital service it took over in October 2002 to 1.5m last summer to a likely 3m by the end of next month. Cable firms bring in a further 2.2m digital TV homes.

Technically, at least one such system is available to 99.4% of households, according to a BBC and Independent Television Commission report from April last year, which suggests that digital TV will be used by 58% to 78% of households in 2007. Eventually, all viewers will have to use it, as the government plans to turn off analogue TV transmissions by 2010.

To some extent, digital TV reaches the groups that the internet doesn't. According to the BBC/ITC report, C2 (skilled manual worker) households are the social group most likely to be users: the professional AB group are most likely to be internet users. And Freeview is attracting senior citizens: last June, the BBC said that about 40% of buyers were over 55.

So the government has been testing digital TV as a way to deliver information. The Pensions Service ran a pilot from May 2002 to March 2003 on satellite and cable. Users felt that the service, which provided information and limited interactive facilities such as ordering leaflets and email inquiries, was a positive development, although some expressed concerns about the security of the system, as well as using the television - normally used to entertain several people - for administering their finances. There were also complaints that interactive services are often slow and prone to crashing. There have been other trials: Hertfordshire county council started a pilot on NTL's local digital cable network as long ago as December 2001.

But the technology will get its biggest group of public-sector users this summer, with the opening of NHS Direct Digital TV. This £15m interactive service will be similar to those provided by the BBC, with teletext-style information bolstered by images and some video content, rather than programmes. It will offer a directory of NHS providers such as GPs and dentists, a database of ailments as well as advice for self-care and healthy living, along the lines of the NHS Direct website at www.nhsdirect.nhs. Eventually, the Department of Health hopes it will accept repeat prescription requests.

NHS Direct plans to appear on all three of the digital TV platforms, although it will start on just one and has given itself until the end of the year to add the others. The need to distribute services as widely as possible may prove a challenge, if the experience of the BBC is anything to go by.

"The technology is different, and the approach of the technology is different," says Richard Cooper, head of technology for BBC new media. "Open TV [used by Sky Digital] allows you to program at a very low level: you can write programs with very complex behaviour. Liberate [used by cable] is closer to a web browser, but with specific extensions to support TV. MHEG-5 [for digital terrestrial] was designed for simple multimedia presentation on TV screens."

However, the situation is improving. "The complexity of authoring for such different platforms means that various solutions are being developed that enable you, to some extent, to author a service once but publish to all platforms," says Cooper. However, "for more complex or cutting-edge services, at the moment, you still have to build it three times".

The BBC's text services were designed separately for each digital TV platform, Cooper says. "As far as possible we provide the same experience on each platform. In practice there are differences: on cable there is more content, on satellite there is more video, and on Freeview - on more modern set-top boxes - it is very fast."

Another difference between the three channels is the availability of a return path, something required for true interactivity. This is easiest on cable, with plenty of capacity in both directions, and possible with Sky, as users are meant to leave their boxes plugged into the phone line, providing a narrowband connection. But there is at present no equivalent for terrestrial television.

Accessibility of digital TV is another problem, with a Department of Trade and Industry report from last September finding that 7.1% of the population are likely to have difficulty using digital TV and recommends training to help set up and use the services; more hardware that combines set-top boxes with TVs; and better-designed remote controls.