It’s 1987 and Syd and Sylvia run Eastbourne Working Mens Club. Syd is the belligerent host, all bad mother-in-law jokes and murdered versions of classic songs. His wife Sylvia is the bit of skirt, something pretty for the punters – and she sings a few songs too. Tonight is going to be different though; Sylvia’s been taking Women’s Studies at evening class, she’s had enough and it’s about time she said something.

The performance opens with two voices arguing loudly offstage. Syd is unhappy that Sylvia wants to try something new, letting her know in no uncertain terms that this is his show, not hers. When solo performer Claudia Jefferies appears as herself to introduce the show, it’s also to warn us that this is an experiment, she’s also watching our reaction. We are being challenged. (And in that spirit, let me also warn you that there is some very challenging language coming up later in this review.)

At first glance this is a musical comedy parody – recognisable songs with new lyrics. Funny, right? But as both Syd and Sylvia, Jefferies goes well beyond parody in a visceral takedown of sexist social mores. The false bonhomie, the dreadful jokes told so badly they’re good, the edge between husband and wife, are all skewered perfectly and dialled up not one notch, but several.

It doesn’t stop. In the “audience participation” section (don’t worry, it won’t be you) a man is objectified and humiliated; it’s over the top of course, but the shock is intensified because it’s a man – the target in these scenarios so often being a woman.

Jefferies is a tremendous performer. She has the boorish Syd – the posture, the dead-eyed stare, the casual entitlement and aggression – nailed down so well it’s chilling. His constant put-downs of Sylvia (she’s no Shirley Bassey, no kids but still covered in stretchmarks) can’t be dismissed as “banter”, but is bullying that’s clearly been going on for years. In turn, Sylvia rejects her traditional role and fights back against years of misogyny. Build Me Up Buttercup becomes “Why do you feel me up, y’fucking cunt” – when Jefferies throws a metaphorical punch, she doesn’t miss and hit the wall.

As the show moves on to stories of sexual molestation, using recorded voices describing assaults, the links to the attitudes represented by Syd couldn’t be made more clear. To ram the point home, Jefferies comes out of character at the conclusion to deliver her long list of demands, a repudiation of casual and not-so-casual sexism – “don’t tell me to smile unless you’re planning to make me happy”.

Syd and Sylvia can be an uncomfortable watch at times. Some people loved it, some most definitely didn’t, and I still feel genuinely sickened by aspects of it. But such strong reactions are precisely the reason that we need people like Claudia Jefferies making shows like this. You could say that those that loved it are already converted, and those who hated it never will be – but others, I hope, will go away rethinking assumed positions. And anyway, somebody needs to be out there kicking against the pricks, inspiring others.