Panic, Barbican Pit, London

Puppetry, penises and paper bags: sounds about right for a show about the poster boy of paganism, the priapic goat of the Arcadian greensward, doesn't it? Phelim McDermott, leading light of Improbable, is the perfect Pan, too, gimlet-eyed, round-bellied and naughty.

But this is theatre on the cheap and in the living room, with a scaffolded forest made up of brown paper trees and brown paper bedroom sheets fantasised in the privacy of McDermott's book-lined apartment in Brixton.

With photographic projections, he welcomes us there, abandoning his three nymphs – Angela Clerkin, Lucy Foster and aerial artist Matilda Leyser – to tell us about his prostate problems and addiction to self-help books.

The show combines stand-up confessional schtick with theatrical story-telling, and the mix is only partly successful, sometimes curdling into dullness before leaping to life with some Pan gobbet or adventure, such as Pan struggling to find a resting place for a huge stick-and-straw appendage that is giving him no peace of mind at all.

McDermott emphasises this tormented side of Pan at the expense of the sheer delight of his penile persona. He glumly tells us that he's added up the number of women he's slept with – it's a Don Juan list of 147 – and that the one who turned him down was the girl on the bus to school, the Number 147. He finds her on Facebook, takes her to lunch and seduces her in a park.

Do we believe this? If we do, does it matter? You might be more alarmed by McDermott's self-help books – Don't Be Nice, Be Real; Dare to Win, and so on – that fill eight paper bags, bags that later form masks for the three nymphs.

This is not so much rough theatre as rough-and-ready theatre, and it does have a sort of faded charm while also coming across as slightly cliché-ridden and shop-soiled, a bit like McDermott himself. He's still a very funny man, a natural clown, a rogue, which is good.

But there is an element of contrivance when he demonstrates his affliction of "labyrinthitis", or loss of any sense of balance, by pushing Matilda around the stage before letting slip that Matilda is, in fact, his girlfriend (is that number 148?). She descends in a dream from paper trees in a distinctly un-erotic harness; or maybe that's erotic and I'm in the wrong theatre.

Yet all the good work is nearly undone by a tedious anecdote about meeting a Pan-like, goatee-bearded Buffalo Bill lookalike in a bar in Columbus, Ohio: Pan needs to take a grip, and not just in a rude way.

To 16 May (020 7638 8891; barbican.org.uk )