A notice in Summertown library reads: Remember when you had the time to read? You still do. Try an audio book!' Many people leading busy lives, with long commutes to work, piles of ironing, or both, are rediscovering the pleasure of books through listening to them.

Since the 1990s audio books have been a growing niche industry within publishing, now worth around £70m a year.

Large publishers such as Penguin and HarperCollins have audio book divisions, but Isis Publishing in Osney Mead, Oxford, has specialised in the field and is now the UK's leading producer of unabridged audio books.

Founded in 1988, today it has 18 employees in Oxford and 25 at its sister company Soundings, in Whitley Bay, North Tyneside.

Editorial manager Emma Higgs said: "I get annoyed about abridgements. Often I don't think users are even aware that they are listening to an abridgement, on just two or three cassettes, and only getting about a third of a book.

"They miss out on what it is all about; the dynamics of the plot, and the highs and lows of emotion."

Audio books were originally developed for visually-impaired people, many of them elderly.

The RNIB (Royal National Institute for the Blind) began making recordings on shellac discs in 1935.

This group of people is still the most important listenership for audio books, although the leisure listener market is expanding.

Because unabridged books cost £30-60, most people borrow them from libraries, and library sales are Isis Publishing's main source of income.

Social inclusion legislation, designed to make books accessible to everyone, means that all British libraries now stock audio books and some even run special book groups.

Mrs Higgs manages two audio book lists - Isis and Soundings -and buys the rights to 16 new titles for each list every month, making the yearly total of new titles 384. There is also a backlist of about 5,000 titles.

The Soundings list is what people traditionally think of as audio books - family sagas where an orphaned girl makes her way in the world, and cosy' crime.

The Isis list is more contemporary, with more hardboiled crime and more literary titles.

Fiction predominates but the range also includes history, memoirs, and biography. To complement its audio books, Isis produces printed books in large print versions, for visually-impaired people.

The books are recorded in studios on the company premises. Occasionally, authors read their own work but it is far more usual for them to be read by actors with specialist training as voice artists.

Mrs Higgs said: "They have to be very good at characterisation and have real voice skill to keep someone listening for ten hours plus.

"They need staying power to do the recording, because however much preparation they do, they are still effectively sight-reading.

"And you want someone who doesn't fluff' too much!"

The master recordings are then edited to remove mistakes, sent for proof-listening to ensure they are complete and accurate, and copied on to cassettes and CDs, either at Isis or, for large cassette orders, at Soundings. The cover design is done in-house.

The company keeps stocks of all its back titles and, for a small fee, offers a replacement service, so that if one cassette or CD becomes damaged the book can be repaired.

Because elderly listeners are less likely to have CD players, cassette recordings have continued to be important in audio books years after they disappeared in the music industry.

But this year sales of CDs overtook those of cassettes for the first time. This reflects the increase in people listening in their cars, which no longer generally have cassette players.

Another development is the sale of audio books as computer downloads.

Isis general manager Pauline Horne said: "The potential of download has excited the industry more than e-books.

"It is quite a leap to think of curling up with an e-book. With audio books it is just the delivery that is different."

Isis Publishing has won accolades at the Spoken Word Awards run by the Audiobook Publishing Association, most recently in 2005 for Preethi Nair's Hundred Shades of White read by Aileen Gonslaves. Its most popular authors currently include Alexander McCall Smith, Martina Cole, Ian Rankin, James Patterson, Danielle Steele, and Barbara Taylor Bradford.

Mrs Higgs said: "Audio book publishing has been small and unrecognised in the publishing industry, but it is getting a much higher profile.

"Trade magazines such as The Bookseller and Publishing News now review audio books, as well as print books."

No longer seen as second best more and more people are appreciating the special appeal of the spoken word.

Miss Horne added: "After all, we are brought up with people reading us stories."

Contact: Isis Publishing, 0800 731 5637, www.isis-publishing.co.uk