In one of those unspoken rules of TV drama, whenever our hero finds themselves up against competition from within their own ranks it must always come in the form of somebody cast as their extreme opposite.

If the protagonist is a workaday, pedestrian with an unassuming nature, their rival will be exaggeratedly pompous, over-the-top, and self-obsessed. Similarly should the subject themselves be larger-than-life, arrogant or headstrong, their immediate foe tends to end up painted as laughably dull, blinkered and timid. The business of jockeying for power and influence within the same institution – especially one of law and order, or government – doesn’t often develop on screen in the most subtle of ways. Pretenders to the throne of everyone from Jack Regan to Francis Urquhart never posed that much of a threat as they were never seen to operate on or even acknowledge their opponent’s terms, only their own. The champ rarely, and perhaps frustratingly, faced a usurper of truly equal mettle.

So it was in this new BBC film, and in particular its depiction of the rivalry between Prime Minister Stanley Baldwin and the supposedly over-the-hill Winston Churchill MP during the mid-1930s. Unconvinced by talk of a resurgent, re-armed Nazi Germany, Derek Jacobi’s Baldwin sighed and fretted and rolled his eyes upwards while pressing his hands to his forehead. His incompetence was implied not so much through what he said, which was little, but his crushed, rather pathetic and simpering demeanour. Albert Finney’s Churchill, meanwhile, shot down his nemesis by swaggering into view, cheeks flushed, barking out orders and insults, utterly convinced by his own argument. He was Churchill, so he had to be right. Moreover this was a view, we were told, entertained by a cast numbering less than two, which was all the more reason to be impressed by the man’s arrogance and fortitude. “I am a great man”, he snapped at a snivelling Ronnie Barker (playing David Inches, his butler), before melodramatically slamming the door in his face.

The practice of re-telling history through character-led drama necessarily involves a smoothening out of some awkward, spiky edges. There isn’t time for reams of rather earnest, lengthy analysis, referencing multiple points of view and complex claims and counter-claims; there are visuals and soundbites and music and special effects to play with, not a solitary blackboard and piece of chalk. Consequently the political condition of inter-war Britain suggested in The Gathering Storm placed Baldwin and the entire Tory Government in one, hapless, German-appeasing corner, with an isolated, depressed Winston Churchill – conveniently blessed with, as it later proved, frighteningly accurate foresight – in another. There was no compromise, no halfway house. And because Baldwin was a ditherer, he was in the wrong.

Derek Jacobi did his best to add a bit more substance to his role than the rickety script allowed, but the fact his character had been so obviously and rather unimaginatively made the lame duck of the piece almost undermined the point of the whole film. Being so two-dimensional, it was a portrayal too expected, too predictable, to exist effectively alongside the carefully developed and decidedly three-dimensional realisation of Churchill. Finney, however, relished playing up the numerous complex and infectious aspects of his role, and which the film self-consciously sought to focus on right from the start. This was a fantastic effort at bringing the past back to life, and in the process both replacing and re-energising the bundle of clichés attached to the man over the last half-century. A pity, then, he wasn’t served with supporting cast that could have thrown Churchill’s current plight and own confusing past, into a more engaging, exciting light.

Vanessa Redgrave, playing his wife Clementine, was a dominant and compelling figure during the first half hour of the play, until plot dictated she disappear off round the world, leaving both Churchill and the storyline reeling and disjointed. The below stairs staff, headed up by Ronnie Barker, were often pulled off screen the moment they began to enjoy a decent and absorbing bit of dialogue. With Churchill’s parliamentary peers mostly confined to – literally – heckling from the wings, it ended up left to friend and mysterious secret agent Desmond Morton (Jim Broadbent) to fill the role of cipher, properly elucidating the significance of Baldwin and Churchill’s actions and sketching in some crucial context.

His was ultimately the most important part of all, as he had the job of delivering lines compressing the entire course of events in Germany since 1918 and the end of World War I into five-second long sentences without sounding too contrived or laughably unnatural. Here’s where that essential process of smoothing out history’s knots and double bluffs sometimes breaks down. In the right hands – such as Broadbent – compulsory, ultra-concise updates don’t sound forced or as though their narrator is trying too hard. You appreciate their point and purpose, especially when the overall structure is that of the TV film (90 minutes) rather than a mini-series (such as Band of Brothers, which made full and effective use of its 10 hour running time to tackle World War II in a manner – just as much through sensation and emotion as narrative – that would not have been possible here).

But other times that task can become a curse rather than a blessing. A rather messy subplot, involving the passing of classified documents concerning Germany’s armed forces to Churchill, meant much scene-setting and summarising had to also be done by Linus Roache, playing junior government minister Ralph Wigram. His clumsy, mock-pious mini-speeches, nailing the inception, likely development and tragic dénouement of the Third Reich in less than 100 words, tumbled onto the screen in an embarrassingly jarring manner. This was classroom-style preaching and lecturing, totally at-odds with the mood and tone of the rest of the film. We later saw his character become depressed with the turn of events, and suddenly end up dead on the bathroom floor, a climax that had little impact for being indifferently trailed and poorly realised.

The conclusion of this highly absorbing, exceptionally-filmed yet also somewhat unpleasant study of one-upmanship was a bizarre one: the outbreak of World War II, but presented as a triumph, with soaring music, upbeat speeches and much cheering. Churchill was shown almost dancing for joy as he dashed up the steps of the Admiralty building to resume the position – head of the Royal Navy – he held during World War I. A caption then reminded us of how he went on to lead the country to victory in 1945.

Sure, the coming of war proved Churchill to have been right all along, but there seemed little need for the film-makers to be so proud of the fact. A more resonant statement had come just a few minutes earlier, in the shape of the real-life voice of Neville Chamberlain, declaring war on Germany in perhaps one of the most affecting radio broadcasts of the 20th century. This effectively summed up the absolute devastating significance and irony of everything we’d witnessed over the preceding hour and a half. After this, yet another scene of Churchill guffawing felt almost irrelevant.