But is it Pam-proof?

The effectiveness of a firewall is usually proportional to its price, but the best are reputed to be very reliable. 'We trust firewalls enough to put a $6 billion business on the Internet,' says Matt Reid at Sun, where 23,000 staff all have access to the Internet from their desks.

The other security issue is whether staff with Internet access will spend all their time planning their holidays or downloading Pamela Anderson screen savers. It is much the same argument as was used against PCs in the 1980s, when it was feared people would waste hours playing Pac Man, but they didn't. An increasing number of businesses are coming round to the idea that the potential benefits are worth the risk.

Above all, an intranet is a medium for publishing information. Some businesses take this literally and use intranets to replace traditional paper for reports, manuals and other internal documents, ensuring that staff always have access to the latest versions.

The benefit is often something as simple as creating a better sense of community in the firm through staff magazines, discussion forums and so on. 'So many people are completely ignorant of what their company actually does,' says Bowbrick. 'An intranet can change all that.'

Unipalm Pipex has a typical selection of information on its own intranet.

This includes the internal telephone list complete with people's mug-shots and potted biographies; company policy statements and information such as car mileage rates; ready-made sales and PR presentations; a social noticeboard designed to take the heat off the internal email system which is reserved for business messages; a 'wanted' and 'for sale' bulletin board; a quality assurance form to encourage staff feedback on company issues; and, as if that weren't already enough, links to other Web sites.

Even the smallest businesses can benefit, especially if they are geographically dispersed. Hypereality Systems consists of three one-man bands in Cambridge, Hastings and Macclesfield (with its intranet servers located on Anglesey). The proprietors use their intranet for sharing up-to-date job lists, price lists accounting information, and for collaborating on the Web pages they create for clients before they are published on the World Wide Web.

Ask a user what's most useful about the intranet and the most likely response is speedy access to reliable information. 'So often you sit down and you think, I don't really know where to start. I could make five phone calls before I find the right person,' says Philip Connolly, corporate positioning manager at Glaxo Wellcome. 'It's wonderful to be able to go into the intranet and search for the topic you want. It saves so much time.'

It usually takes Connolly less than a minute to track down the information using a combination of keyword searches, bookmarks and knowledge of the intranet's layout - less time than it would take to walk to a filing cabinet and pull out a paper folder.

Connolly also believes in the quality of the information he finds. 'I have confidence in the reliability of the intranet,' he says. 'I know I've gone to the best source there is. If I went to my own filing cabinet it might be out of date.'