Mayor Carcetti has a problem. White, youthful and reforming, he has just entered office to discover that the previous administration of Baltimore (Democrat, like him) had allowed an overspend in the schools budget of $54 million.

The Governor of Maryland will partly bail him out, but only on terms that threaten his own ambitions to govern the state, and will be unpopular with civic leaders of the city's black majority. Carcetti spurns help and starts to cut his budgets, including that of the police. Everything begins to go to hell.

So begins series 5 of The Wire, the latest series to be described as the best television ever made, and not without justification. “Level with them!”, I find myself screaming at Carcetti (and thus, I suppose, at the scriptwriters), “Tell the voters what the problem is. Perhaps they'll understand. I would.” But Carcetti and the scribblers who created him effectively rebuke my naivety by assuming - without debate - that, whatever a politician may do, he may certainly not rely on the electorate to respect his honesty.

Perhaps they're right. Perhaps in real life, as on TV, politicians simply say to themselves that it's a rough old game and has to be played by rough old players. What, after all, do you achieve by overfrankness? Or by living a life of exemplary sincerity?

Last summer the highly non-fictional Chancellor of the Exchequer (if you made him up you'd probably add an interesting characteristic, a facial tic or a habit of quoting Cicero) took a boat trip with a woman journalist. Putting down the oars for a moment, he told her that the economic circumstances facing Britain were “arguably the worst they've been in 60 years. And I think it's going to be more profound and long-lasting than people thought.”

This straightforwardness naturally earned him the plaudits of a media hungry for truth and of colleagues desperate for plain-speaking. And I am the Queen of Romania.

One typical broadsheet headline the next day was “Labour in turmoil over Alistair Darling gaffe”, “Instead of reassuring voters, the Chancellor risked compounding the crisis”, the report said, adding that Mr Darling had “hinted at rifts” (he hadn't) and that “his comments are seen at Westminster as a barely concealed attack on Ed Balls, Brown's closest confidant” (seen by whom?). “Darling sends pound diving,” headlined another paper, erroneously.

Other anonymous persons were not impressed with Mr Darling. A “senior Labour figure, who was out canvassing voters” was quoted as saying that “we are out on the doorstep, trying to reassure people, at the same time as Darling is telling them we are all doomed”. Not much truth premium there. Or, as “one senior Labour figure” told a Scottish newspaper, “he has made a complete arse of it”.

Last week, in one of those autophagous moments that we in the media indulge in, it transpired that this last anonymous person was none other than the wicked Damian McBride, although we weren't told that at the time. The creature McBride had busied himself - with the complicity of some journalists - in punishing the Chancellor for having been uneconomical with the actualité. No wonder that the former Blair aide, Matthew Taylor, was amused to receive calls from “Sunday journalists” asking to be told more about McBride's unpleasantnesses. It was, he said, “a bit like someone saying: ‘Me and my mates have for years been having a very intimate relationship with someone you might vaguely know - what was it like?'.”

All this is a symptom of the mutual catastrophe of trust, in which politicians and journalists are not trusted by the public, and the public is not trusted by politicians and journalists. The public want many things, the almost subliminal logic runs - reassurance, emotional connection, a satisfying narrative - but not the truth.

No recent incident has demonstrated as clearly the trust trap that politicians create for themselves, as what might be called the knife statistics debacle. Because the Government had been caught cooking the books a little in its early days, it began to be assumed that everything it said was wrong. Which meant that even when the Emperor really was wearing sumptuous vestments, little boys everywhere would proclaim his giblets to be unpacked. So Gordon Brown set up the independent UK Statistics Authority to oversee the work of the Office for National Statistics. Anything less McBridey would be hard to imagine.

Then, a few months ago, at the insistence of No10 and against the objections of statisticians, figures seeming to show a fall in knife crime, were released. Sir Michael Scholar, head of the authority, complained loudly: “There is a code designed to prevent political manipulation and my authority was set up to police this code. I am sorry to say the Home Office and No 10 broke these rules.” So, whatever small gain was won by the premature release, the longer-term result was, inevitably, to undermine still further trust in the Government's use of statistics.

But then, bizarrely, the Office for National Statistics itself released, two weeks early, a set of figures on immigration, justifying its actions on the ground of “topicality”. Since this effectively means “newsworthy” it led to suspicions that the statisticans were themselves keen to get a little of the limelight. This, too, seemed to be about getting an easily distracted public's attention, using the even more easily distracted media to do it.

Politicians, in their cups, will agree that they do things simply for fear of how not doing them will look. Recently the former Education Secretary Estelle Morris gave instances of some Labour policies that owed nothing to necessity - such as homework for 5-7 year olds, where the evidence was “that it matters not a jot whether very young children do homework. Were we going to go out and change our policy? No, we were not because... we wanted to sound firm on that.”

So we got unnecessary homework for our kids because the Government thought that we would like them better for it. And probably we did! Maybe it's been rational of government and politicians to pander to our irrationalities, believing that we are more likely to punish than reward honesty.

Even so, readers may feel, as I do, that we are coming to the end of this double pretence. Perhaps the incredible volume of information generated by the infotech revolution - the capacity to check on claims or film policemen or discover hidden e-mails - make it harder for one's tender illusions to survive and be nurtured by those in authority. It could be that the price to be paid for dishonesty and evasion - ours and theirs - is going up. I hope so, because it's time the culture changed.

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