THE NEW SERIES of The Thick Of It begins tonight, three years since we last saw the characters on our screens. In the interim, government and opposition have swapped places but, other than that, I suspect we will find that not much has changed.

The hapless ex-minister Nicola Murray has been elected as Leader of the Opposition, much to the derision of her own party and delight of her opponents; meanwhile the government lurches from crisis to crisis, making up policy on the back of envelopes as they go along. Throw in a couple of topical twists - ministers are facing a Leveson-style inquiry, and have been forced to cohabit with a junior coalition partner to govern (“Well, I say partner,” the Ken Clarke-ish Peter Mannion grumbles irritably into his phone: “He's Lewis, I'm Morse”), and it’s clear that Armando Ianucci’s irresistible art is once again imitating life.

Just as instructive is the way in which this cynical, foul-mouthed take on Westminster has wormed its way into the mainstream of our political discourse.

When I started blogging in 2005, the salty language of online political writers was regularly castigated in the pages of our quality newspapers. We were attacked for everything under the sun; nihilism, misogyny, stupidity, and above all a corrosive cynicism that was, it was claimed, destroying faith in our politics, with grandees of journalism like Polly Toynbee loudly decrying those who were pursuing an “anti-politics” agenda.

Fast forward a few years and the most feted political comedy of recent times is guilty of all these assumptions, and more besides. The politicians who inhabit the world of The Thick Of It are everything we ever painted them to be; portrayed as shiftless, stupid, headline-obsessed grotesques, and mocked in the foulest of tongues. But no longer is this a minority report. The show which started on the ratings wasteland of BBC Four is now prime time on BBC2 on Saturdays; “omnishambles” is a permanent part of the Westminster lexicon; and Ianucci has even been awarded an OBE, a remarkable instance of our political classes feeding the hand that bites them.

So, what changed? Undoubtedly, the declining calibre of our politicians is one underlying cause. Once, we were served by people of quality, of conviction, of rectitude. They were people who had done things, real things – had fought in wars, had written scholarly works, created successful businesses – and those of us who had done no such things were forced to admit that there was something there for us to look up to. Even with those we mocked - the Michael Foots, the Roy Jenkinses - we could appreciate their strength of conviction and common decency, even as we chortled at their political ineptitude and wondered how someone so steeped in learning could be so wrong about everything. Compared to those men – and, of course, the occasional Lady - the Prescotts, Hunts and Huhnes of this day and age are, rightly, weighed in the balance and found wanting.

But it’s more than that, I think. All political eras have contained their dunces and scoundrels, lechers and drunks. And even this one has impressive and admirable figures, though admittedly you have to search pretty fucking hard to find them. No, what changed was two things.

First, and foremost, it is indisputably true that we now assume, as a matter of course, that our politicians lie to us on a regular basis.

This sea-change is a direct result of the Blair government, the most mendacious British administration of modern times, a government where lying was raised almost to the level of an art form. How could it have been otherwise, when their guiding triumvirate – Blair, Mandelson and Campbell (the original Malcolm Tucker) – were born liars, to whom falsehoods came as natural as breathing? How could it have been otherwise, when Gordon Brown devoted so much energy to trying to screw his superior out of a job that when he finally succeeded, he didn’t have a single idea what to do with his newly acquired position? Lying was their default position; contempt for the voters their daily touchstone. They poisoned British politics, and we are still feeling the effects.

The second major factor, of course, was the expenses scandal. For years, excitable libertarian bloggers like myself used to noisily opine that all our politicians were crooks and thieves, while (again) newspaper columnists, friends and therapists told us, in effect, not to be so childish. On the day the Daily Telegraph unveiled the full scale of the fraud perpetrated on us, that particular canard was exposed for the nonsense it was. I don’t mind admitting that I felt a certain vindication: “We Told You So” was the lone headline on my blog for a few days, and we had, and it was true.

To paraphrase David Frost’s famous observation on television, for well over a decade we were governed by people we wouldn’t have allowed into our homes. What did we expect?

Despite everything, I hoped that this Government would be better. I still do. But it is testing my patience, as it is surely testing yours. And when I look at Armando Ianucci’s new series I expect that I will, in Orwell’s phrase, look from pig to man, and from man to pig, and from pig to man again, and find it impossible to say which is which. Art imitates life. Or is it the other way around?