Once upon a time, in an altogether more innocent age, a reporter's job was to turn up at a politician's speech and, well, report it. These days, the journalist waits by the phone to be favoured with a call from the politician's press people, who will offer a taste, or "trail", of what their boss is to say for publication before it is actually said. For media purposes, the speech itself becomes largely redundant.

This change has worked well for New Labour, which may not have invented the dark art but has certainly perfected it. The preferred interpretation of the speech is established upfront, optimal soundbites are planted, and the journalist, congenitally incapable of resisting a scoop, falls for it every time. And before you mention pots and kettles, I by no means exclude myself from this stricture.

But has the point come for the government where media manipulation of this kind is no longer delivering, where it has in fact become counter-productive? Are news organisations so determined to nail ministers in certain policy areas, such as health, that even the choicest of fruits served up by press officers and advisers are turned into rotten tomatoes to be hurled back at their superiors?

Take last week's coverage of the launch by health secretary Patricia Hewitt of the commissioning framework for health and wellbeing. By any yardstick, the framework is A Good Thing, seeking, as it does, to shift the NHS from being just a sickness service; to encourage greater collaboration between health agencies and councils; and, crucially, to inspire and empower GPs and their colleagues to prescribe social care and other non-health services for their patients. Astonishingly, though, the plans have been ridiculed.

How did this happen? Blame the trail. This was placed in the Sunday Times, 48 hours before the framework's launch, and carried on the newspaper's front page. Hewitt, it said, would allow GPs to prescribe free air-conditioning units for patients with breathing problems arising from chronic obstructive pulmonary disease. Almost 1m people could be eligible for the £500 units.

While there may have been an initial plan to mention such an idea, as the kind of thing GPs might think about doing under the framework, it never featured in the minister's speech when she unveiled the document. But the hare was up and running. On the Monday, the Sun was proclaiming: "Air-con on the NHS", and the Daily Mail, pointing out that the NHS was "massively in debt", declared: "Lung patients get their own cooling units."

By Tuesday, the day of the launch, the Times's columnist Martin Samuel was penning 969 words of bile on the general themes of the (wretched) state of the NHS, the inability of Labour to run a whelk stall, and Hewitt's "promise of a chilled climate for a million incurable wheezers this summer". Samuel, sports writer of the year, concluded: "Air conditioning to be provided by people that can't find you a bed? Don't hold your breath."

This, in the main comment pages of the Times, was damaging enough. But the next day, the Mail was back on the theme with Hamish Meldrum, who chairs the British Medical Association's GPs' committee and who - if quoted accurately - really should have known better, saying "it beggars belief that a government that has lost its way with the NHS wants the service to provide air-conditioning". Final result: Sensible Advancement of Preventive Healthcare 0, Ludicrous Hysteria 1 (Department of Health own goal).

There's a theory around that, if and when he becomes prime minister, Gordon Brown will appoint a health secretary adept at keeping the NHS quiet - no initiatives, no speeches, absolutely no trails. You could hardly blame him.

· David Brindle is the Guardian's public services editor

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