Music lovers do it every night: Somewhere in the audience - and maybe next to you - sits a fanatic. Susan Loppert meets the concert-goers who will listen to everything

She's always there - a diminutive grey-haired gamine, rather like Picasso's portrait of Gertrude Stein, always in motion like some inquisitive bird, and always alone.

Over the years I have noticed her at every recital, concert, Prom or opera I have attended; at the Wigmore Hall she always sits in the front, on the right by the artists' door. She was backstage recently at the Boris Godunov Prom, and hugging Andras Schiff in the green room of the Queen Elizabeth Hall. She is also to be seen at private views of grand exhibitions - the recent Magritte at the Hayward Gallery, for instance. Speculation is rife and everyone knows about her without knowing her: she is Hungarian, French, German; a psychoanalyst or psychiatrist or psychotherapist; friend and hostess to the Takacs Quartet, Thomas Allen, Anne Sofie von Otter; learning the piano with the teacher of Brendel's children.

After a while, because I kept seeing her, I began to think I knew her; more, that since she liked what I liked, she must be like me. Who is she? The answer is a paradox: for all her conspicuous presence at everything, she is a very private person who chooses to remain a cipher, and who is there on her own 'because I want to listen - I am immensely permeable and don't want to be burdened with people's perceptions'.

There are many other legendary or obsessional presences in London audiences, alone but not lonely; there's Tom, who is at every performance at Covent Garden; when the season is over, he is at the Coliseum or the Proms every night. No one knows where he is or what he does on Good Friday and Christmas Day. There's Heather, described as a babushka, who never misses a performance of the Royal Ballet, and claims to have discovered Anthony Dowell. There's the man in evening dress standing out from the scruffy promenaders at every Prom.

At what point does passion become obsession? Is it omnivorous or selective? Peter Gregory is motivated by endless curiosity, boundless energy, and the need for only four hours' sleep a night. So far this year, he has been to 75 concerts, 53 operas, 82 plays, 16 musicals, 108 films, 90 exhibitions, 58 stately homes, 38 rugby union and 14 rugby league matches, and watched 59 days of cricket.

Gregory is a tall man - 6ft 7in - and, as a taxation accountant, has the habit of listing and tallying; he is 48, with thick unruly pepper-and-salt hair and blue eyes behind thick spectacles. He is not married ('I wouldn't have time, would I?') but shares his flat behind Brompton Oratory with a woman (a singer with the D'Oyly Carte Company who last year sang in the chorus at Bayreuth and is usually on tour) and 30 years' accumulated programmes.

The previous week, he had been to I Capuleti ed i Montecchi at Covent Garden, a concert at the BMIC premises in Stratford Place ('they're free') which included music by Reger, Water Music at the Cockpit Theatre ('quite obtuse but I love fringe theatre'), a film at the French Institute and, 'by mistake', White Men Can't Jump ('billed as truly wonderful but truly dreadful; I usually go by Derek Malcolm'); on the Saturday he had been to two rugby matches: Harlequin in the morning, England v Canada in the afternoon at Wembley, the Herbert Howells concert in the evening followed by a late film, Polanski's Silver Moon; even later, at home, he watched that evening's episode of Testament of Youth on video. Early on Sunday morning he drove to Poole in the company of Radios 3 and 4 to go walking with friends in the Purbecks, returning to London on Monday morning; that evening he managed two films, and the following evening was the Sinfonietta birthday concert. 'Call this the Diary of a Madman if you like,' he says disarmingly.

He loves English music - Bax, Bridge, Rubbra, Havergal Brian ('I'm not sure about him'), and, particularly, lesser-known composers like Granville Bantock, John Foulds, Harold Truscott; he is 'trying to be fair to contemporary music - I have to rely on my ear since I don't read music', and likes Steve Martland, Mark-Anthony Turnage, 'even Brian Ferneyhough'. And although 'I don't pretend to be an expert on anything, Hugh Wood's Third String Quartet is the best quartet of the last 15 years'. French music is a passion - he was a member of the Massenet Society for years - and Martin Cooper's French Music from the Death of Berlioz to the Death of Faure his bible. And he prefers hearing works at music colleges which are rarely performed and therefore more interesting: 'I'd go to the Milton Keynes Orchestra playing Raff rather than most orchestral concerts.'

He is a loner but not shy - 'I'll talk to anyone about anything' - and knows many actors and musicians and most critics ('John Amis thinks I'm Simon Bainbridge and always asks what I'm writing'). He is also, despite having lost his job at the disgraced BCCI and been out of work for 11 months, a patron and angel in a small way: he has supported the Garden Venture for new operas, the Nash Ensemble and Lontano, and has put money - disastrously, he cheerfully admits - into plays transferring from the King's Head to the West End. He always sits in the cheapest seats - 'I saw Cats for pounds 9]' - and reckons to spend pounds 300 a month on tickets. An omnivorous digestion?

Dick M is a pensioner who has refined his tastes over the years, but who nevertheless spends pounds 50 a week on his passion; rather more this month, as he bought two front amphitheatre tickets at pounds 50 for Otello (he usually sits in the slips) and, 'against my principles', became a patron of the new Wigmore Hall. He will be going to all the re- opening festival concerts, although he is torn between the Margaret Price recital and Simon Rattle conducting two Nielsen Symphonies at the Barbican. The Wigmore Hall is one of his heavens - 'I remember the great days of the Griller Quartet'. Others are Opera North (last season he heard Schreker's Der ferne Klang, Nielsen's Maskarade, Boris Godunov, The Thieving Magpie, La finta giardiniera, and Paul Griffiths' Mozart patchwork, The Jewel Box); Glyndebourne (he has been a member since 1956, when he heard the performance of Idomeneo which led to his 'proprietary interest' in the opera - 'I'll have the march at my funeral'); Berlioz - 'I'm the guardian of the flame' - and the now defunct Berlioz Festival at Lyons ('the mayor of Lyons was a kind of Heseltine and didn't like Berlioz'); he is contributing an article on L'Enfance du Christ to the new Prommers' magazine, Strictly off the Record. This season, he went to 32 Proms - the most ever.

His interest in music was fostered by masters at Emanuel School and he has been going to concerts ever since he could afford it; Covent Garden once a month cost half a crown. A retired commercial barrister, he is a surprising 72: his receding brown hair is untouched by grey, and he looks a fiftyish, thinner Philip Larkin. He has some of Larkin's mordant manner too. Sound bites: 'I used to go to Scottish Opera but there's something limited about Scots and music'; 'Solti is soulless - like Karajan, he puts the light on the orchestra rather than the singers'; 'performances on authentic instruments can be travesties: Melvyn Tan is very precious and managed to play Opus 90 without realising it's one of the great pieces of music'; 'I'm not a collector - of performances or programmes'.

Although music has taken over - 'I used to read passionately; novels, biography, philosophy, history' - Dick M is also keen on architecture and painting ('I'm a 'Friend' of everything - the Tate, RA, BM') and the theatre; he loved Diana Rigg's Medea at the Almeida, where the Chorus sang rather than spoke, and the RSC's Theban plays at the Barbican ('The Greeks are pretty misogynistic'). He deplores the cult of the producer - 'I want to see Shakespeare, not Trevor Nunn; Mozart, not Peter Sellars.' No films and no television ('I'm usually 20 years behind with technological developments'), but Radio 3 and, occasionally, Radio 4.

Yvonne Pegler listens only to Radio 4 on one of her seven stereo cassette- radio-cum-CD players; she also has a large 1950s radiogram, 'a collector's item', and 40 years' worth of programmes 'dating from oratorios in Hornsey Town Hall'. An ample dimpled blonde d'un certain age, always immaculate in billowing Liberty prints and costume jewellery, with beautifully manicured scarlet nails, she has occupied the same front row seat in the Festival Hall for two nights out of three since 1959. She has even become a statistic in the Policy Studies Institute's survey, which cites her as proof that numbers of tickets sold do not necessarily indicate that large numbers of people attend classical music concerts.

An Examiner in the Patent Office who read Maths at Queen Mary College, she began going to the Festival Hall as a schoolgirl in 1951 when her father's firm furnished the curtains; he sat in the bar while she went to the concert, and the habit of going alone has continued.

She spends around pounds 300 monthly, not only on the South Bank, but at the Barbican (even though 'it's like a council estate and the acoustic's awful'); the previous week had included not only the Herbert Howells concert, Andrew Davis / Elgar / Hugh Wood / Joanna MacGregor, and Radu Lupu playing under the conductor she dubs Frankly Worse than Most, but Dave Brubeck and Eartha Kitt and the Inkspots; she recently went to the Chippendales in a giggle of girls and loved the show: it was 'suggestive, but not in a nasty way'.

She prefers to hear the human voice at home on one of her 3,000 tapes or 400 CDS: 'in a way I want them to sing for me alone'. Her gods, now that Klemperer and Boult are gone, are Giulini, Haitink, Tennstedt, Ashkenazy, and Richter. 'With the lights dimmed he plays only for me, and all the old magic is there.' She has been to Salzburg, and travelled with the LSO on tour to Italy. She reads the critics of the Times and Telegraph 'to see whether they agree with me' and has a cooked breakfast every day ('the fat you have in the morning is broken down more easily'); on the occasional night in, she indulges her other passion, dressmaking. That weekend, she was looking forward to 'a grubby concert (Raymond Gubbay will kill me)'.

Is this obsessional running from self, or running towards enlightenment? Terminal loneliness, or beatific fulfilment? If the pleasure principle doesn't rule, will pain triumph? The answer seems deceptively simple - as one said to me, 'Music isn't my passion: it's me'.