Penguin working on eBooks for Apple's iPad

However, until sales rise, Makinson said the company would be "creating a lot of our content as applications, for sale on app stores and HTML, rather than in eBooks".

Makinson's comments come as the publisher launched its first 'Digi-Novel'.

Dark Origins by Anthony E Zuiker is part of the Level 26 serial-killer thriller series of books and will be accompanied by a website featuring exclusive content.

Penguin says that during the book, readers are directed to the website and required to enter codes that unlock 'cyber-bridges' - such as videos that put the reader "inside the minds of a twisted torture-murderer and the man sent to take him down".The publisher said the exclusive content was designed to enrich the reader's experience, but is not essential to read and enjoy the story.

See also: British Library to offer 65,000 free eBooks