Lately it seems as though musical producers are working their way through the alphabet for films to ruin, starting with Amélie and Back to the Future before moving on to Cronenberg’s Crash (to the tune of ‘Flash’ by Queen).

It is one thing to add songs to a classic tale such as Matilda, but adapting a cult film is a trickier proposition. These are movies beloved not necessarily for their stories but for their performances, dialogue and idiosyncrasies, in other words the films themselves. Trying to bring Heathers to Broadway is like making Donnie Darko the Musical, and even as I write that I know it’s only a matter of time. So in a sense Heathers the Musical (currently touring the UK) was always doomed but it barely displays so much as a superficial understanding of the 1989 original, seemingly made by someone who had the premise and costumes described to them by a person with a vested interest in its failure or possibly a strong speech impediment.

As though acknowledging the impossibility of recasting the iconic Veronica Sawyer (Winona Ryder’s greatest role), the stage version changes the character from sarcastic misanthrope to generic Musical theatre person. Her partner in crime J.D. (Christian Slater’s greatest role) is similarly flattened, answering the question nobody asked: what is Heathers without weirdos? The outcome looks closer to a high school production of Mean Girls punctuated by random recitations of classic lines from Heathers that jar with the tacky musical tone, like pulling a cracker on Christmas Day to find a dead wasp and a joke about Madeleine McCann.

The songs are equally incongruous, ranging from quotes that sound stupid out of the movie’s context (‘Our Love is God’) to bizarre numbers about sweets (‘Candy Store’) that appear to have accidentally wandered in from a neighbouring theatre showing Charlie and the Chocolate Factory. Most egregious is when J.D. sings about his love of slushies in ‘Freeze Your Brain’, which would be awful even if it was relevant to the film (where it is Veronica who asks for a slushy). Not only does the number have nothing to do with Heathers, it has nothing to do with anything.

That sense of irrelevance pervades the whole show, so weirdly disconnected from everything that made the movie great that you might as well be watching Greased Lightnin’ fly away at the end of Crash the Musical.