It is Max Newman’s (Alan Cox) finest hour. Despite a flighty political past and dubious tabloid reputation – very consciously modelled on Boris Johnson – he is the darling of the voting public. The Conservative leader and current prime minister has recently resigned, and Max is his obvious replacement.

Eleanor Hopkirk (Joanna Bending) – Tory parliamentary whip – has managed to dupe Max into a meeting with his lone leadership rival, Dan Regan (Laurence Dobiesz). There she hopes she will use Regan, a promising young colt of a junior minister, not only to help her unhorse Max, but to convince the bumbling old rogue to stand down voluntarily. Unlikely as it sounds, playwrights Robert Khan and Tom Salinsky have given her an impressive ace in the hole that does the trick. Being a woman in parliament is still a strong disadvantage, she explains. Even other female MPs are considered enemies. But this just makes Eleanor – in her position of power within the party – more formidable: she has learned to play by, exploit and supplant the rules of the men’s political games.

The venue for the tete-a-tete is a forgotten Westminster backroom. The landlines have been cut off, there is no mobile signal; we are miles from the political and public front line. All this lays the foundations for what is Kingmaker’s most frightening assertion about UK democracy: all the important political battles are fought and decisions made in private elitist bunkers like this.

Like a good Shakespearean tragic hero, Max is introduced to us before he enters. When he does so, it is with a charismatic bound. Though undoubtedly a rogue, Cox does an outstanding job making it obvious why the man is so popular. But he has a dangerous side to say the least. At the heart of Kingmaker is a question: how monstrously must these people have behaved privately to land the top public positions? The problem: the man has survived everything. It’s his flaws that make him human, and his humanity makes people vote for him. He is politically invincible.

The experience as a whole is a paradox. The political swordplay is sharp and witty throughout, but most enjoyable because the characters can’t evade each other in the room’s tight confines. They are forced to attack at all times. But as a play to watch on the eve of the General Election, behind my involuntary grin it didn’t half make uncomfortable viewing. None of the characters redeem themselves. Their morality is muddied and sullied as we progress, and the portrait we are left with is a deep shade of faecal brown. There is a limpness to Kingmaker’s climax that serves the writer’s purpose perfectly. The flaccid flailings of the defeated party in their death throws are about as lively as we get here, and that is because everything genuinely human died over the course of the previous 50 minutes. Who would give these monsters the keys to the country?

Kingmaker is playing at Arts Theatre until 23 May. For tickets and more information, see the Kingmaker website. Photo by Jeremy Abrahams.