An opening night at the theatre is usually filled with magic, excitement and drama.

But behind the curtain someone will be watching the audience nervously, possibly wringing their hands with worry. That person is the producer, onto whose shoulders the ultimate success or failure of a show falls.

Kenny Wax has been bringing shows to the West End for more than 25 years, working his way up from general manager at the King’s Head in Islington to creating the multi Olivier-winning musical Top Hat. His latest project is The Comedy About the Bank Robbery which previews at the Criterion Theatre from March 31.

“You have to be very patient and understanding,” says the Hadley Wood resident of his job. “You deal with a lot of creative and artistic people and you have to be able to get up when you are knocked down and deal with a lot of disappointments and frustrations.”

The business studies graduate moved to London in 1987 and worked for Dixons head office in Edgware for a year before realising he had fallen in love with showbusiness and giving himself a year to peruse his dream.

He worked as an usher at the Theatre Royal Drury Lane, at theatre advertising agency Dewynters and for Cameron Mackintosh as a runner before setting up his own company in 1995.

Kenny has produced shows such as The Witches of Eastwick starring Marti Pellow, Aspects of Love starring David Essex and Rain Man starring Neil Morrisey as well as numerous children’s shows including The Gruffalo’s Child and Room On The Broom.

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Much like the Wizard in the wonderful world of Oz, Kenny has to pull many strings behind the scenes to make a show appear like magic on a stage and the first task is to find a possible hit from the dozens of pitches he gets sent each month.

He remembers back in 2013 when a friend invited him to see a show at Trafalgar Studios.

“It was an audience of about 100, a one-act show on a set they had built themselves and was a very modest production of about an hour. I sat there on a Thursday afternoon, not expecting very much but it was very funny indeed and people around me were absolutely crying with laughter.”

That show was The Play That Goes Wrong, which had been written by three Lamda graduates in their spare time under the name Mischief Theatre and originally called Murder at Christmas.

Kenny recalls: “I think I did feel they really had something and when it went on tour we could see it did.

“The touring market is very driven by stars and it didn’t have anyone famous but people were drawn by the title.”

The show is now a smash-hit, with celebrities such as Simon Cowell, Ellie Goulding and Harrison Ford having been spotted in the audience, and has been sold out for the last few months for every performance.

“That is incredible in the West End, even the big musicals don’t do that, they have peaks and troughs,” says Kenny who was raised in Manchester and whose first experience of theatre was going to the Royal Exchange with his parents.

“You do it long enough and every now and again something comes around that works and people love it, which sells. Often you can do fabulous shows and nobody comes to see them – I have done a few of those in my time.”

The father-of-three says of things going wrong: “There isn’t much these days that can’t be sorted with money or time. But when that means an audience doesn’t get to see a show, when you have to cancel performances, that’s awful.”

He adds: “The worst thing is when shows don’t sell and you have invested a lot of money and so have your friends and investors. I get sales sent through electronically every hour of the day so I can keep track and if something isn’t working it’s clear.

“The last time it happened was a show on tour, I won’t mention the name as it’s a bit indiscreet, and I was the show manager. I was getting paid but the producers were losing tens of thousands of pounds a week and there was nothing we could do. If we had closed the show early he would have been in breach of all the theatre contracts.”

Kenny and Mischief are hoping to capitalise on the success of The Play That Goes Wrong and follow-up Peter Pan Goes Wrong with third show The Comedy About a Bank Robbery but he knows there is no such thing as a sure-fire hit.

“Previously the shows have started in fringe theatres, “ says the Fawlty Towers fan. “The first one was going for a year before we knew anything about it, so they were tried and tested. This one feels a lot more exposed because we haven’t done that fringe thing. It’s a lot more exciting because it’s a much bigger play than they have done before, much more ambitious, with a bigger budget, so it’s exciting but a bit scary.”

Drumming up the money is still the hardest part of the job for him but Kenny also oversees the script, set, marketing, press, promotions, ticketing consultant and production consultant and decided where to spend the budgets and place adverts. He also has to deal with numerous artistic temperaments on a day to day basis.

“Some people behave fantastically badly and I just don’t want to work with them again. Screaming and shouting and hissy fits. I just don’t have time for it.”

And it is very emotional for him when his hard work doesn’t pay off.

“I care very much about my shows. I had a big musical called Top Hat in the West End and there was documentary made on Channel 4, which showed us recasting and winning a bunch of Oliviers and then the box office not improving and then me having to go in and tell the cast we were going to have to take the show off.

“When you are seeing 70 people out of work it is very sad.”

That is a rare occurrence for Kenny though who has about 20 projects on the go at the moment including taking Hetty Feather to New York, working with Sally Cookson on a project based on an 1950s Oscar winning film and developing a four million pound musical for the West End in 2018.

So does he still get nervous ahead of opening night?

“You just hope something major and unexpected doesn’t go wrong.”

The Comedy About A Bank Robbery previews at Criterion Theatre, Jermyn Street, SW1Y 4XA, from March 31. Details: 0844 847 1778, bankrobberycomedy.com