So, is this information or entertainment?

Just as our hospitals cut waiting lists by selecting easily treatable patients, TV channels hit curr

Each year, the government provides British broadcasters with cash and other privileges worth around £4bn. In return, it demands a say in what they put out. Once, a shortage of channels required their content to be managed; moreover, charging consumers for individual services has been impractical. Yet digital transmission, due to be universal for television by 2010, will enable us to buy, or advertisers to support, whatever we want, just as happens now in the world of print. So in a supposedly free society, why doesn't the state just butt out?

There is an answer. Broadcasting is indeed special. Instantaneous, going into virtually every home and able to combine sound with moving image, it is just too valuable to be dedicated solely to the demands of individuals. Collectively, we have further vital tasks for it that neither consumers nor advertisers would sustain by themselves. Entertaining may be broadcasting's primary function, but society also needs it to educate and inform.

Unfortunately, this argument is looking weaker by the day, as fulfilling public duties fades from our broadcasters' list of priorities. As new channels lure viewers away, advertising-funded broadcasters with public responsibilities are having to look to their ratings. That includes state-owned Channel 4, as well as ITV. Instead of taking up the slack, the BBC, though richer than ever before, has chosen to play the same game. Its success in doing so has increased the pressure on its advertising-funded rivals.

This cycle is set to intensify. If we allow it to, broadcasting's public dimension will steadily lose its meaning, even if its outward forms are allowed to survive. Some have already given up on it. In a recent book entitled The Decline and Fall of Public Service Broadcasting, the communications guru Michael Tracey pronounced its subject "a corpse on leave". Suddenly, however, fingers are prodding the carcass with a view to resuscitation.

Over the past year, the Guardian and a leftish think-tank have staged a conference on public service broadcasting; centrist and right-wing think-tanks alike have published studies on the subject; and the new communications regulator, Ofcom, has been asked to take a look. The expiry of the BBC's royal charter in 2006 presents an opportunity to break into the spiral of decline. The government has decided to mount a charter review aimed at testing the present system to destruction. The Conservatives have set up their own inquiry team (of which I am a member). Sadly, this burgeoning interest does not seem altogether welcome to some of public broadcasting's apparently most impassioned supporters.

Already, academia, the right-on press and the Radio 4 communion are drawing up their wagons in defence of the status quo. The mood, however, is more of tetchy resentment at being challenged than of eagerness to present a compelling case. If you're lucky, you may get a glib put-down. Public service broadcasting makes the good popular and the popular good. Got it? Now piss off. Or, you may elicit the mystical defence. Purposes are beyond definition, while to try to measure outcomes is sacrilege. Only those summoned to this high calling can formulate its sacraments.

Either stratagem implies that apparent anomalies must simply be accepted. Should the BBC really be making programmes indistinguishable from those that the market supplies just to maintain support for the regressive tax that pays for them? But of course, dear boy: the world is a complicated place. Pseudo-economic mumbo-jumbo is on tap for those who like it. Yet talk of "public goods", "experience goods" and "economies of scale" turns out to cloak arguments that, if applied elsewhere, would place much of the British economy in a Soviet-style public sector.

Behind what often seems like a smokescreen hides the despairing view that a genuine case for the public broadcast voice can no longer be made: it would be bound to sound unfashionably paternalistic. So change must be fended off by inducing inertia through confusion, or perhaps by mobilising the polite classes in defence of the subsidised cultural booty, from The Archers to Antiques Roadshow, with which the system currently endows them.

Unfortunately, sectional interest is even less likely than bluster or obscurantism to impress the hard-nosed policy wonks who will soon be taking the subject apart. Yet arguments for public service broadcasting have never been easier to make. Political disengagement demands an infusion of civic purpose. The ravages of individualism call for the reinforcement of social cohesion. Deepening ignorance cries out for education. Broadcasting is uniquely equipped to take on such tasks. However, to retain its entitlement to state support, it may have to do a better job of actually fulfilling such functions, rather than merely pretending to.

Measures to enforce compliance with public needs are supposed to be in place already. Commercial public broadcasters (in their licences), Channel 4 (in the Broadcasting Act) and the BBC (in its "Agreement" with the government) are all required to pursue a long list of worthy-sounding objectives. These range from bland abstractions such as "quality" and "diversity" to quotas for certain kinds of programming. Unfortunately, as elsewhere in the public service, attempts to control output from outside provoke counter-measures.

Hospitals cut waiting lists by selecting easy-to-treat patients, teachers "teach the test" and chief constables cook the crime figures. Public broadcasters call Tonight With Trevor McDonald current affairs and fill so-called arts programmes with celebrity gossip. Supposed orgies of enlightenment, hastily assembled when (as now) the heat is on, prove stronger on hype than delivery. Yet such "reform" of the regulatory machinery as is currently in prospect will make it so "light touch" that providers will be allowed to set their own public objectives and report on their own success in achieving them.

Surely a public broadcasting system, as much as any other public service, should have clearly stated goals reflecting genuine needs. It should ensure that these goals are pursued with vigour, not evaded wherever possible. It should drive up standards and assess outcomes, subjectively where necessary. It should rely on a rational funding mechanism and be able to show it provides value for money. Instead of replicating what the market provides, it should complement it.

Our present system fails these tests. Left to itself, it seems certain to degenerate further, and thus become harder to defend as the costs it imposes grow increasingly irritating. For public broadcasting, change is now a necessary ally rather than a threat.