For the past few months, I have been harbouring a guilty secret. Of a Monday night, I occasionally sneak down the road with my guitar and play a few songs at an open mic night in the basement room of a local Irish pub.*

This revelation usually provokes a mixture of sympathy, horror and mirth - rather as if had disclosed that I enjoy making love to horses. However, given that this week is officially London Songwriters Week, and the capital's thriving open mic scene is proving a fertile breeding ground for stars such as Kate Nash, and Jamie T (though hopefully not with each other), I feel finally able to come out.

According to the invaluable Virtually Acoustic Club website, there are 258 open mic nights in London alone, providing a valuable support network for delusional dilettantes like me and a vital first rung of the ladder for those set on a musical career. The format is usually the same: show up, sign your name down and wait your turn to bestow the the audience with two or three compositions.

The popularity of such nights is one positive symptom of the demise of the traditional music industry. While the industry frets about falling record sales, sales of acoustic guitars are hitting levels not seen since the folk boom of the Sixties. Amateur musicians are able to take advantage of the internet and are content to find an outlet, however modest, for their talents - which, alas, often are pretty modest.

Of course, there are moments of ignoble thrusting that would shame an X-Factor contestant. But the nights are usually free, friendly, socially diverse and in spite of the preening, the caterwauling, the faux-estuary accents, the men who cover Jack Johnson and the women who cover Tracy Chapman, there is always at least one person who blows your socks off.

An unassuming woman in thick glasses, an anorak and hiking boots, turns up at the Irish pub most weeks, and launches into heartbreaking a-capella blues songs. A few times we have been graced by the notoriously fearsome film director Tony Kaye, maker of American History X. Film industry workers are apparently known to wear T-shirts saying "I worked with Tony Kaye and survived"; the shy man we saw played a couple of Bowie-esque ballads and shuffled meekly away.

But if the open mic teaches you one thing it is that there are a lot of people out there who are slightly talented songwriters, competent guitarists and pleasant singers. And the process which plucks out somebody like Kate Nash and decrees she of all people should become a star is entirely random. Maddeningly so, for there are plenty as talented than she, and a night spent in a basement bar in Crouch End or Herne Hill is ample proof of this.

But the best open mic performers are not in it for the fame. My favourite is Silver Sam, a well-spoken old duffer who looks like a kindly headmaster and sings hilariously explicit songs about his sexual prowess. He may not make it to Brixton Academy, but once a week, for ten minutes, he is a superstar. Or considerably more times a week, if you believe the boasts of his lyrics.

* Ryan's Bar in Stoke Newington, to be precise, where Sophie keeps a happy home (one detail I chose not to give when this piece made its unhappy way into print).