Corridors of power are never brightly lit in television drama. They’re always enveloped in a dank fustiness, a fog of gloomy upholstery and even gloomier faces, both looking as if they’ve been trapped there for decades. But they’ve rarely been as murky as they appear in The Alan Clark Diaries.

A veritable pea-souper seems to be permanently moving through Clark’s Palace of Westminster, wrapping its subjects in dismal shrouds of weariness and treachery. Whitehall is no better, depicted on-screen with all the soul and warmth of a Victorian municipal baths, where huge panelled doors swing shut like prison gates and the sun only ventures through a tiny skylight once a year. It’s a wonderfully atmospheric creation: a shadowy warren of crumpled mandarins sporting identical grey suits and wrinkled brows. It’s also the perfect setting for Clark’s meandering, portentous prose; each of his famously pithy epithets and insults finds an echo or resonance in such a desolate location, bouncing around the walls and through the television set to leave you completely caught up in the man’s plight.

It’s a fine tribute to poise and judgement of the production team that this muddy adaptation of the man’s exhaustive journals never once exchanges deft observational storytelling for petty political point scoring. Doggedly faithful to Clark’s original text, the programme presents you with the picture of a man who’s his own judge and jury, who frequently condemns himself out of his own mouth, seems to change his mind over the most trivial of things within minutes, and swears profusely. Whatever your own feelings towards Alan Clark or the political turmoil he finds himself alternately observing and contriving, there’s a depth and dimensionality to his fictionalised incarnation, rooted in the almost ethereal drabness of the world in which he moves, that makes for enthralling entertainment.

The fact that by design it’s a personalised, one-sided take on recent history allows for an unusually generous dose of caricature that all political dramas thrive upon but rarely pull off convincingly. Scriptwriter and director Jon Jones offers us endless recreations of Clark’s pen portraits which, given they were often critical, mostly indiscreet and nearly always rude, compound the grim facades of Westminster with an ensemble of comic grotesques. A brilliant supporting cast exaggerate those defects Clark chose to make his obsessions in order for events to unfold in a suitably arresting fashion. Transferring something that originally existed in the most private and literal of forms into a richly-visual, multi-character serial necessarily involves a degree of licence in both plot and characterisation. Here the process is carried off with aplomb, converting one man’s late-night scribblings into an expertly fashioned production – one where dialogue and location work in tandem to create a carnival of duplicity and bedlam.

In fact, The Alan Clark Diaries often has the feel of a circus: a roll call of luminaries doing set turns and party pieces, a grand arena in the shape of Parliament itself, and an inspired use of non-specific yet slightly familiar classical music, conferring both a whimsical and operatic status on proceedings. And centre stage, orchestrating everything we see and hear, is Clark himself.

Even after just one episode it was difficult to imagine anyone other than John Hurt playing the man, such was the speed and confidence he utterly occupied the role and became, if not the actual Clark, but the perfect embodiment of Clark-as-diarist. Given the entire programme is built around voiceovers lifted almost verbatim from the original manuscripts, it’s Hurt’s superbly dusty drawl that sets up then sustains the theme and tone of each instalment. When he’s on camera, Hurt plays Clark as a constantly shambling and crest-fallen runner-up, his very countenance smacking of forever being denied a shot at the top job. An air of suspecting that everyone’s out to get him, and of life cruelly denying him what he feels is rightfully his, pervades Hurt’s every glance and shuffle (traits that are frequently universal amongst history’s famed diarists). Even when he walks down a corridor Hurt is articulating a very specific state of mind, most commonly – through cumbersome swings of the arm and shifty-eyed stares – a sense of being utterly fed up.

Hurt is a joy to watch, because he’s clearly relishing the part and feels just as comfortable depicting Clark meandering along all those dimly-lit passages as prowling about the family country estate. Those scenes that are out of doors, however, come across just as bleak and monochrome as those confined behind four walls. It’s as if the camera’s – or Clark’s – eye bleaches everything out, so rather than vibrant greens, reds and yellows framing his sprawling gardens, everywhere is slate-grey and ashen. It’s a useful reminder that all that we’re seeing on screen is, in theory, supposed to be entirely from one man’s perspective. Similarly, while the fact that the interior of every single plane Clark flies on looks the same implies the production budget was small, it could equally imply that for Clark every single plane he flew on did literally look the same – nicely convenient for all concerned.

The one concession to actual reality, and a virtue of what Hurt himself has gone on the record to complain were paltry production costs, are the contemporary news reports which pepper proceedings. Not only do these serve as evocative montages telegraphed from an increasingly remote era – the old “fish finger” Nine O’clock News title sequence, for instance – but they help frame the substance of each episode with a bit of background, filling in times, dates and places while neatly circumventing the need for any clumsy contextualising conversations where figures are seen unconvincingly swapping blindingly obvious information for the sake of scene-setting. Interestingly the only point we get to see the face of the Prime Minister is in these archive clips; the actress who plays her on-screen is filmed solely from the back, a device nicely complementing Clark’s predilection for referring to his boss forever as “the lady” or “herself”.

There’s virtually nothing to fault here. A small team of people have worked in perfect synchronicity to create a hugely absorbing recreation of one man’s take on an era of British politics, conferring neither hero nor victim status on their subject and instead offering up an expert study of a complex character moving through complex times. Grimy corridors and tatty swivel chairs have rarely looked so thrilling.