'It looks like there's been a mix-up. We only have a reservation for one double room." The receptionist at the Montrose Abbey bent again to the pencilled jottings on her bookings page. "No, it's a definite mix-up," she announced firmly, as though laying the mistake squarely on the broad shoulders of the God of Chance rather than on the narrow incompetence of her hotel's reservations system. "Would you mind sharing?" She smiled encouragingly at me and my festival companion, Dennis. "We have a twin-bedded single room." She made it sound so simple. Like opting for bacon and egg because of the definite mix-up there'd been over the kippers.

"I'd really rather not share." My statement hung in the air. Why couldn't I share? Was I a serial bed-wetter? The secret owner of wooden leg? "It's just that I'm six foot two," I blurted unnecessarily. "I can't manage a single bed. I need space." "Honestly Laurie, I don't mind if you don't," said Dennis whose everyday capacity for empathy wouldn't disgrace a ventriloquist's dummy.

I did mind. I minded so much that I left a bewildered Dennis to his own individual towels and sewing kit and tramped the streets of Edinburgh in search of a room I could call my own. What was the alternative? How could I tell Dennis that I wouldn't be able to sleep a wink as long as I knew there was another person laying only a locker's width away in an identical single bed?

I don't need a psychoanalyst to advise me on this phobia. It proceeds quite logically from my childhood years at a Catholic boarding school where every single little boy longed for the moment when the dormitory priest finished reading to us from the life of some poor masochistic saint and announced that it was time for lights out. That was the sacramental signal, the starting gun for mass masturbation. I don't know how the culture developed but somehow or other this nocturnally assembled bunch of fifty eleven-year-olds had collectively decided that this was a ritual which must be followed with a degree of conscientiousness otherwise solely reserved for weekly Communion.

But it was a very wary form of wanking: the slightest noise would alert the priest who sat in a lighted room at the far end of the dormitory. So every boy had to guard against the possibility of rustling sheets by making a little tent with their open knees within which they could silently satisfy their desires. It made for quite a scene. There were nights when our dormitory resembled nothing so much as the eve of the Battle of Agincourt.

That injunction to be silent extended to consummation. We all became practised in the art of concealing the slightest grunt or groan of pleasure. But there was more. There must be no evidence of our deviance on the sheets. For most boys there was only one receptacle to hand: the tiny plastic bags normally used for storing our postage stamp 'swaps'. It was quite a feat of silent endeavour to manage such a precise discharge. But the consequences of failure were too terrible to envisage. Every morning the priest in charge held a laundry inspection. Any suspicious sheet was dragged off the bed and taken to the end of the dormitory. "Look here, boys," he would say triumphantly, holding up it up in front of his face so we could see the shadow of his finger prodding the stain. "You know what this is, boys. This is a dead baby."

But when even this prospect failed to reduce the number of boys who owned up to self-abuse in confession, more drastic steps were taken. Six boys, including myself, were made masturbation monitors. Our single task was to lie awake at night listening out for telltale sounds: the least rustle of a sheet or the slightest sigh of pleasure or the merest crackle of plastic being hastily resealed. We could only allow ourselves to sleep when thick silence reigned.

How could I ever have explained all that to good-hearted literal Dennis? How could I have told him that my childhood conditioning would almost certainly ensure that I'd be listening half the night for the slightest sound that might resemble self-abuse? But worse than that. How could I possibly have warned him in advance that if I awoke suddenly in the early hours in a disoriented condition and heard any telltale shuffling, he might find himself summarily ejected from his bed and marched off, incriminating sheet tucked underneath his arm, to the receptionist.

All of which is why my next two Festival nights were spent at a grim B&B on the wrong side of the station in a room so bare and comfortless that I even wished in the moments before I dozed off that Dennis could have been there with me. Just as long, of course, as he kept his knees together.