Say you have been summoned to a lab and tasked with formulating the perfect British comedy. The details of the lab are not necessary for this, so stop asking. Stop asking who is funding this great experiment. It does not matter why they have chosen you, instead of someone qualified. We’re getting off topic. No, there are no windows. Well yes, fine, I suppose you could call it a “bunker” then. The point is: you have been summoned to a lab and tasked with formulating the perfect British comedy. It will be on BBC Two. So you guide your hand past the conical flask marked Mel & Sue and you dawdle over the petri dish with Jack Whitehall’s Dad in it, but finally you decide to add a big slosh of Tim Key to the broth (for this analogy to work, you really have to imagine a broth). Obviously, every action has an equal and opposite reaction so you need someone to balance out the – yes this is all getting away from me very rapidly, thank you! – pH, or something, so you decide upon Daisy May Cooper. To, uh, brew the broth in a giant still? Something like that, anyway. To do that thing you decide upon the Gibbons brothers as writers, after they did such an exceptional job of reinventing the Alan Partridge universe with This Time. As a catalyst you are allowed one little dash of Steve Coogan as a script consultant. For colour, you get a bit of Jessica Hynes. And for a concept, you have, “a witchfinder and a suspected witch go on a Trains, Planes and Automobiles-style odd-couple journey across the English countryside circa 1645”. Perfect, perfect, perfect! You have made every correct choice you possibly could. Right let’s put that in the oven for a bit and … ah. That’s a shame. It’s turned out really bad. It doesn’t make sense that The Witchfinder (BBC Two, from Tuesday) is as underwhelming as it is, because as mentioned above: all the ingredients were there. After being the go-to punchline guy in every single British comedy over the past 15 years, Tim Key was well overdue a good leading role, but this one isn’t right for him: his trademark bumbliness rubs up against the need of his character, witchfinder Gideon Bannister, to be liked and feared and respected. (As a thought experiment, if you get bored watching – which you will – imagine every line said by Coogan instead, and it does work better.) Cooper, so achingly funny in This Country, is superb as the suspected witch Thomasine Gooch, but woefully underused: the few bright spots in the first two episodes are when she does that blunt, straight-faced patter she’s so good at, but there is nowhere near enough of it. Hynes is completely wasted, and various other comic actors are given barely-there cameos and no punchlines to deliver. If you are fond of the witchfinder episode of Inside No 9 from a few years ago and are expecting more of the same, keep expecting. If you were hoping The Witchfinder might follow along the lines of Ghosts – another perfectly cast, slightly high-concept BBC comedy – think again. Ghosts remembered to make every character interesting and funny in their own right. The Witchfinder replaced all that with a too-slow-moving murder-mystery. You’re right, it’s hard to make people laugh. I read the comments section beneath these columns, sometimes, and see that sentiment expressed a lot. But to even try to start making people laugh – the thrust of every comedy, no? – you do have to actually write some jokes. The Witchfinder expends too much energy trying to tell some story – Key and Cooper have to go here this week, then they meet an obstacle, then they have to figure their way round it – and relies too much on the natural comic gifts of the two actors without giving them enough funny to play with. Key’s character is slimily unlikable, pathetically unbrave and greedily ambitious: there’s nothing redeemable to make me enjoy watching him for six episodes. Cooper’s disaffected one-liners could be the star of the show, but too often she’s used as a prop to get Key out of a self-imposed scrape. Hard to know who to blame for this really, but … well, no, I do. It’s your fault. You mixed all these ingredients up, in that lab I put you in, remember? You forgot to add jokes, you fool! Try again, and this time add some Whitehall!