Delia who? Ask any of the twenty-first century musicians who revere her. Paul Hartnoll, for instance, of Orbital: 'She made the Doctor Who theme, the single most important piece of electronic music. It still sounds as fresh as a daisy today. I listen to it and I still can't work out how she did it, after nearly 20 years of messing around with electronics. The secret died with her.'

In 1963, Delia Derbyshire was a studio manager at the Radiophonic Workshop, a BBC department in Maida Vale established to provide special sound for experimental radio programmes. She had been trying to break into the field for years. A Cambridge music and maths graduate, she was turned down for a job at Decca Records on the grounds that women were not employed in recording studios. Officially, all attachments to the Workshop were temporary, as the BBC feared that overexposing their employees to electronic sounds might induce neurological damage. History, however, intervened to extend her tenure.

In the summer before the Kennedy assassination, Derbyshire was assigned to arrange the theme music for a new BBC drama series about the occupants of a time-travelling police box. The prolific TV composer Ron Grainer had already constructed its familiar tune, but it was Derbyshire who turned it into a revolutionary electronic work. Stormy swooshes, uncanny howls and an insistent beat conveyed the impression that something was rumbling towards the listener from a distant dimension. 'Did I really write this?' asked Grainer, on hearing the results. 'Most of it,' Derbyshire replied.

Her colleague Brian Hodgson, who created the sound of the Tardis by scraping a Yale key across the strings of a dismembered piano, describes her methods: 'She would take an object, a lampshade, say, and hit it, muffle it and hit it again, hang it up and rub it so it sang like a wine glass. She got all the tones she could out of it and then would filter them, treat them, torture them, create different textures, and meticulously put them back together again, to make abstract, beautiful atonal music.'

During the following decade, Derbyshire enjoyed creative relationships with Stockhausen, Peter Maxwell Davies, Brian Jones and Paul McCartney. She cut a bizarre pop record with Anthony Newley; engineered, with Yoko Ono, a 'happening' in Trafalgar Square; and in concert with Brian Hodgson and the musician David Vorhaus generated White Noise, a classic album of 1960s electronica. In the process, she gained a reputation as an energetic and incorruptible innovator.

'Early electronic music,' explains Mark Ayres, a friend and fellow Doctor Who composer, 'was random atmospheres and sounds generated by electronic equipment, or sounds created by tape manipulation - recorded, looped, re-pitched, and physically cut to create music. In the early Seventies, we got the first synthesisers - machines that could generate those sounds within themselves, with keyboards that helped you to organise them. The problem with these was that they were inherently unstable: if somebody opened the door and the temperature changed, they would go out of tune.'

Derbyshire was depressed by the increasing dominance of the synthesiser, which encouraged electronic musicians to abandon atonal work. 'Delia was at her best surrounded by bits of tape,' reflects Ayres. 'In 1973, she was asked to redo the Doctor Who theme with a Delaware [an early synthesiser], and she was very unhappy with the results.'

Shortly after this experience, she left the Radiophonic Workshop, moved out of London and took a job laying pipes for British Gas. As the years passed, this vanishing act and her continued silence amplified her cult status. 'Because she was no longer working,' explains Ayres, 'and few people knew what had happened to her, she was simply this evocative name behind these extraordinary sounds. She became a rather mysterious, romantic figure, which I think she thought was rather funny.'

'I imagined her as an Open University lecturer,' recalls Paul Hartnoll. 'That if I went round her house she'd have a man's shirt on and her hair in a late Sixties fashion. [Her colleague] Malcolm Clarke would be there with his big hair and sideburns, and offer you a Peter Stuyvesant. I imagined her to be quite strait-laced, and used to wonder if she was, because the Radiophonic Workshop music was so mental.'

Derbyshire died last year, aged 64, just as she was being rediscovered by a new generation of practitioner-fans: the Chemical Brothers, Aphex Twin, Sonic Boom, Bobby Bird. Blur have reinterpreted her most famous work, a recording of which is to be launched inside next year's Mars Express interplanetary probe. Orbital's rendition is now an indispensable part of their live set - although Paul Hartnoll modestly insists that 'ours is like the Joe Loss version in comparison'.

Rory Hamilton and Jon Rogers's project, Generic Sci-Fi Quarry, might have formed Delia Derbyshire's comeback. But the letter Mark Ayres wrote to invite her to take part was left unopened on her doormat as she lay dying in a Northamptonshire hospital. The event has become a tribute to her memory, with sound elements supplied by her former colleagues: Ayres, Brian Hodgson, Peter Howell, Paddy Kingsland.

In preparation for the quarry event, Ayres is busily feeding video images through a frequency analyser that converts their constituent colours and luminosities into sound. A principal source has been the visual howlaround produced by pointing a video camera at its own monitor, the technique that produced the original Doctor Who titles. Such practices hark back to the days when Derbyshire and her Radiophonic Workshop technicians used reversed and reverberated toilet flushes to furnish the roars of robotic Yeti, and harvested the howls of the fearsome swamp-dwelling Drashigs from the noise of screeching rubber tyres.

Of all her former collaborators, it was Hodgson who knew her best. 'It was a relationship that delighted and infuriated us both. We drove each other mad. She was a conceptualist. She could think through wonderful ideas, but the technology was never there. But right at the end it was just beginning to happen. She once said to me, "I'm having to make too many compromises." And that hurt her more than anything else.'

The Radiophonic Workshop was closed in 1997, a casualty of Birtist rationalisation. But down in the bottom of an Oxfordshire quarry, two doctors are preparing for an event that will resurrect its pioneering spirit, and that of its most celebrated member. Jon Rogers flips open his laptop and demonstrates some of the computer animations which will bombard the senses of the event's attendees.

'We're going to plunge it into darkness and terrify everyone with weird sounds,' explains Hamilton. 'We're going to project a photograph of the quarry wall on to the quarry wall, and warp it. You'll feel as if the shape of the quarry is changing; that it's travelling through time and space.' He turns to Dr Rogers. 'Give him your soundbite,' he urges. 'Oh yeah,' exclaims his collaborator. 'And there'll be no sofa to hide behind.'