Better Late than never in New York

The lights dimmed and 800 pupils dilated, each one absorbing the reflected light from an empty desk, two cheap-looking chairs and a painting of the New York City skyline. A booming voice tore through the silence. "It's The Late Show, with Da-avid Letterma-an!"

Last night I was watching this show; tonight I'm in it.

Hours earlier, we had been typical tourists, taking photographs in Times Square. A young man approached carrying a notepad and wearing a belt that matched his umbrella. "Would you guys like to be on the David Letterman show?" he asked. "Yeah, okay," we replied.

After giving our details we were handed a green slip and directed towards the Ed Sullivan Theatre.

We walked excitedly to our destination, and were greeted by a line of umbrellas snaking around the building. From underneath each, a hand was visible, grasping tightly on to the soggy remnants of green slips of paper.

The faces we could see reflected our own crestfallen expressions. As I looked up into the driving rain, an enormous picture of Letterman smiled back at me.

We inched to the head of the line. A throng of youngsters in Late Show anoraks awaited us. I handed over my driver's licence. "Noo Zeelind huh? Lord of the Rings, right? Straight in and listen carefully. Next!"

A wave of over-exuberance washed over us as we entered the lobby. Sane-looking, well-dressed, middle-aged people attempted to out-whoop each other, snorting with laughter at any stimulus. It sounded like a monkey enclosure.

We handed over our ticket and were told that "for some reason" we had been chosen for a different line.

A blue sticker was attached to our pass. Our whoop-less performance led us to assume the "chosen line" would lead to a side exit and a re-introduction to the harsh New York weather.

As we shuffled away from the crowd towards a smaller group, another youthful face approached and began to whisper.

"Okay, you guys have been chosen for the front rows." My cynicism turned to self-satisfaction. I was special.

"I don't know why they picked you guys. It could be that you smiled a lot or just because you dress nicely." My cynicism returned.

After killing an hour before show-time we returned and were taken directly through to a small room behind the theatre doors.

The chief 20-something then appeared with final instructions for us.

"Laugh as loud as you can. The louder you laugh, the better Dave will be."

We were then asked to practise our laughter. The group happily obliged, responding with the kind of maniacal cackles usually reserved for mental institutions.

Throughout the process the identity of the guests remained hidden. We were simply told it was a "special night", one we should be very excited about.

Then, the blue wooden doors opened to reveal one of the iconic images of broadcasting.

As the audience filtered in, up-tempo music was played at deafening levels as a posse of 20-somethings exhorted us to clap along in unison.

First, Paul Shaffer and the band were introduced, rushing out to start playing. Then Letterman appeared before us, dressed in a bespoke suit underpinned with red braces, sparkling white teeth beaming against the tan of a wealthy man.

After a brief chat with the audience he vanished, the band struck up and the opening credits flashed on to monitors strewn around the stage.

From speakers behind us thundered the immortal words: "From New York, the greatest city in the world ..." and "On tonight's show ... Michael Keaton and musical guest Lily Allen". Special night?

Letterman re-appeared for his introductory monologue. The commercial break came, setting in motion a stage invasion. A dozen people appeared from the wings.

During the intermission, Letterman gathered in a close huddle with his warm-up act and producer. They circled the famous desk like generals planning their next assault.

The floor manager raised his fingers indicating 10 seconds to airtime. The stage cleared and Letterman sat bolt upright at his desk, warming up his facial muscles by pursing his lips tight, then stretching his mouth as wide as it would go, like someone with a mouthful of hot food.

As the music subsided, Keaton was introduced. Having never seen a film star before, I had the cliched preconceptions of glamour, style and unimpeachable self-belief.

Entrance stage left. On he hobbled, his left foot in plaster, shuffling along on crutches, briefly raising his hand in acknowledgement.

After a carefully scripted segment explaining how Keaton's injury was caused rescuing children from a burning orphanage, the two chatted with the chemistry of close friends. Keaton was charming, funny and generous, allowing Letterman to riff at will and enabling free-flowing conversation to take precedence over plugging his film.

Another break arrived and the stage was flooded once more. As the interval ended, the band, drowning out continued conversation between the two stars, stopped abruptly.

Keaton, who had been leaning over towards his host as if sharing a secret, snapped back into his chair.

Letterman's voice became partially audible.

"Wow, I didn't know he'd done that."

"It's happened before," replied Keaton.

What? What had happened? To whom? I felt like I was inches away from discovering the most salacious piece of gossip imaginable. Before I could digest the possibilities, the interview re-started and Hollywood's dirty laundry was cleared to one side.

Keaton plugged his latest film, and then gave a friendly wave to the crowd as he was guided off stage.

Then, the most shocking element of the night. Stagehands prepared for the musical guest. To move equipment on stage the famous New York City backdrop was withdrawn. As the set drew back, my curiosity raced. What would I see? The green room? The hustle and bustle of executive producers? A half-dressed Michael Keaton?

No. A scene reminiscent of the storeroom of a 1970s department store. Shelves laden with dark brown crates and boxes. What looked like the building's original wall panels carried the ingrained dirt and nicotine stains left by 70 years of stagehands.

One of the iconic sets in television history was essentially a warehouse with pretty curtains.

Lily Allen then fluttered on stage with surprising meekness. As her eyes widened with anxiety, band members approached with supportive hugs. Her time came and she gave a faultless live performance.

Letterman signed off and the stage cleared in seconds. He returned moments later with a brief "thank you and goodnight" - and it was over.

Milliseconds later we were blinded by spotlights. As our eyes regained focus, we were ordered out with ruthless impatience.

"Out, out, let's go."

The doors opened and we were out in the rain and the harsh sound of doors slamming shut behind us.