Some men will go to any lengths to get a part

Cole Moreton attends auditions for a full-frontal London show

This is filth. If you are at all squeamish about naked men contorting their genitalia for public amusement, please look elsewhere. No other article in this newspaper is likely to mention what my companions call "dick tricks".

Still here? Fine. We are sitting in a cold, damp room above a theatre in King's Cross and a beautiful young man is tugging his remarkable penis. "Could you just step back a bit?" asks David Johnson, a producer of repute. "You'll take my friend's eye out."

Later, he leans back in his chair, chuckling: "That was one of the biggest I have ever seen. It will all be downhill after this."

These are the auditions for a show called Puppetry of the Penis, which started as outrageous street theatre in Australia, became a huge (so to speak) West End attraction and is now playing across the world. "We have four companies," says Simon Bryce. "They will be performing tonight in New South Wales, Chicago, Boston and Grimsby. Now we need two more members because the Penises are expanding." So what are they looking for? "Guys who can hold their own."

Puppeteers learn to ignore double entendres, or they'd never finish a conversation. Their audiences are almost all women, who scream as two young men stand on stage in nothing but trainers, socks and beanie hats, and perform eye-watering feats of manipulation such as the Eiffel Tower, the Windsurfer, and the Brain. It's really very simple: they tug and scrunch their private parts into amusing shapes.

People pay good money to see this – the best puppeteers get $1,500 (£950) a week, plus expenses. The creators, two Australians called Simon Morley and David Friend, are said to have become millionaires in the three years since they were unexpectedly big on the Edinburgh Fringe.

David Johnson, who produced the stage version of Trainspotting and whose Auntie and Me is a new West End hit, booked the show for five weeks at the Whitehall Theatre. It ran for five months, attracting Hugh Grant, Elton John and Naomi Campbell. "There is not a whiff of baby oil," he stresses. "The show is not erotic. It gives women the chance to laugh at the male member for 50 minutes without hurting anyone's feelings."

But feelings are going to be hurt today. I am asked to score body, face, "appendage" and puppetry. Size is less important than flexibility. Acting and comedy skills are crucial.

"I posed for Cleopatra's Needle," says the script they are asked to deliver in the style of Priapus, the god of the penis. "I took Napoleon's bone apart and I even taught Nero how to fiddle." If the lines go well there is an awkward moment when the judges watch the auditioner undress, usually in silence, hoping the packaging does not conceal a disappointment.

You don't have to be desperate to get your willy out in public, but it seems to help. Billy has hardly worked since drama school, and after watching him whisper the lines I know why. Mark, a tour guide, came because his mum showed him the advert in The Stage. Alan has done more lap-dancing than acting.

"Ouch," says Grant, trying to do the Hamburger, described among experts as "the dick-tricker's dick trick". The instructions tell you to roll the penis between the testicles, turn on a 90 degree angle, squeeze and hold like any hamburger. "It shouldn't hurt," says David. "If it hurts, don't do it."

The youngest man to audition is 21. The oldest is Dylan, a 37-year-old former public schoolboy who has the best manners. "I won't shake hands," he says, after working up a sweat with his pushing and pulling. "No, don't," says David. "Wave goodbye."

Four potential puppeteers are asked to come back next week and meet David Friend, who will test their skills more thoroughly. There is one clear favourite. "I'd marry him," says one of my fellow judges. "If he'd have me."

There's a heavy, musky scent in the air. The red light from the bar heaters and our being round the back of King's Cross make me feel a bit seedy. The auditions have revealed how varied the human body is and how inherently absurd the taboo parts can look, but I no longer believe nakedness is a great leveller: while it is fascinating to take a long, hard (oh dear) look at other men, I now feel seriously insecure. Then comes the question I dread: "So, do you want to audition?"

I think about the flat stomachs, the jawlines, the biceps and the smooth skin. They were all far better men than me. This afternoon has given me a new sense of perspective. I think about the trick Simon says is the most difficult, because it involves folding your tackle and hiding it. I think about my hour in a toilet cubicle at work going through the manoeuvres in the audition pack (heaven knows who heard all that grunting and gasping), and the realisation that the trick he is talking about, the Slow Emerging Mollusc, is the only one I could do with any panache. Or at all. Maybe I could come on as a novelty act?

There is only one possible answer, and Simon looks mightily relieved to hear it. He won't have to be honest about my manhood or even look at it, which changes any relationship. So I smile and say with equal relief: "Er, no thanks mate. No worries."