I was a 12-year-old choirboy, having an organ lesson from my mildly paedophiliac choirmaster, when the event happened that changed my life for ever. No, not that event. He thrust a piece of music into my hands. “Can you learn this in a week?” he asked. “There’s a wedding next Saturday and I’m away. Time you earned some serious pocket money.”

The piece was the Wedding March from Mendelssohn’s Midsummer Night’s Dream. I hesitate to calculate how many times in the subsequent 41 years I’ve played that opening fanfare and its amazing climactic chord (A minor with an added F sharp – what a stroke of genius!). Sometimes it has been three times in a single Saturday afternoon.

But my choirmaster was right. Being able to play that single piece of music – on everything from rickety village organs and wheezy harmoniums to the thundering pipes of grandiose abbeys – has earned me thousands of pounds of serious pocket money over the decades.

These days, however, the time-honoured formula – Wagner in, Mendelssohn out – is heard a lot less often at church weddings. The top two items on Classic FM Magazine’s new survey of wedding music, for instance, were the Widor Toccata (Charles-Marie Widor actually wrote several flashy organ toccatas, but there’s only one that everyone knows) and Pachelbel’s Canon.

I must say that, as I get older, my heart sinks if I’m asked to supply either. Playing the Widor is like running a 400m race. You are supposed to sprint through the whole thing like a young gazelle, but the distance is just that killing fraction too long, and you end up with cramp in both wrists, and puddles of sweat on the organ keys. Whereas playing the Pachelbel is like experiencing brain death: the same dreary bass line repeated interminably. Still, some marriages are like that, I’m told.

But at least these are “known knowns”, as Donald Rumsfeld might have put it on his wedding day. It’s when couples start using their imagination (about the music, I mean) that organists begin to worry. I’ve been asked to play everything from saccharine pop ballads to The Ride of the Valkyries.

Bitter experience has taught me to keep abreast of the latest film sound-tracks, too. For months after Titanic came out, it seemed, every wedding couple wanted My Heart Will Go On. I wouldn’t have minded if they’d also booked Céline Dion to sing it. Having to accompany a rendition by the best man’s auntie isn’t quite the same experience. Nor even recognisably the same song.

Then there was the teenage bride, seven months pregnant, who requested Lou Reed’s Perfect Day. “It was playing on the radio at the exact moment when this happened,” she told me, patting her bump. Whoa, girl, too much information! I much preferred carrying out the musical whim of an 81-year-old widower, marrying a 76-year-old widow, who asked me to play The Best is Yet to Comeas they walked down the aisle. I hope that the subsequent wedding night proved that the choice wasn’t just wishful thinking.

What organists love about weddings is that it gives us the chance to show off in front of people who are young, glamorously dressed and (in the case of the women) often showing acres of thigh and cleavage. Not exactly your typical Sunday-morning congregation, then.

But sometimes the chance to show off can be carried a little too far. Brides are traditionally late, but I once had to entertain a congregation that was still waiting at 4.25pm for a bride due at 3pm. The limousine had broken down, and the hastily ordered taxi then got stuck in a gridlock on the North Circular.

After an hour I had exhausted all available repertoire and was reduced to improvising on nursery rhymes, music-hall songs, Andrew Lloyd Webber’s greatest hits, anything that came to mind, while a desperate curate kept rushing up with what he thought were encouraging messages: “She’s past Neasden . . . she’s nearly up to the Brent Cross flyover . . . she’s having a quick loo stop at the White Bear . . .”.

Will all this soon be a thing of the past? With camcorder-conscious couples now able to muster locations ranging from castles to cricket pavilions for their nuptial celebrations, social-trend gurus are predicting that church weddings may soon seem as quaint and dated as black-and-white televisions. I think they are mistaken.

There’s nothing like the roar of 2,000-odd organ pipes to stiffen your faltering nerve, calm your thudding heart and brace your quaking knees as you exchange rings, look into each other’s shining eyes, and think: “Oh my gawd, what have I done?”

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