Thousands of inserts are to be placed into library books to promote the clients of advertising agencies.
The inserts will be made available at libraries around the country
The scheme offers advertisers 500,000 inserts in county libraries such as Essex, Dorset, Somerset and also Bromley, in Kent, and Leeds.
It aims to cover the UK by the middle of 2008 with around 3m inserts being made available per month.
The promotion is being run by direct marketing company Howse Jackson Marketing and Brandspace CMS.
Inserts, weighing up to nine grammes, are placed in each book as it is hired from the library, with a single insert allocated per person in order to avoid wastage.
Only one insert campaign will be allowed each month.
Mark Jackson, of Howse Jackson Marketing, said: "Library inserts are innovative, unique and offer audience segments which can be traditionally hard to reach.
"Using library books as an advertising medium provides additional revenue for the libraries to invest in books and therefore allows advertisers to contribute directly to local communities."
'Need for sensitivity'
Guy Daines, director of policy at the Chartered Institute of Library and Information Professionals, had mixed feelings about the plan.
"Like every other public institution, finding other income sources is important for libraries and many have been offering readers free bookmarks sponsored by local firms for some time," Mr Daines said.
"We're not necessarily against the idea of inserts in principle, but I can see a number of potential problems.
"Any product placement would have to be incredibly sensitive - in children's books, for example, or with adverts for something like a funeral director.
"There's also people's general dislike of junk mail to consider and the sheer time it will take for librarians to insert them all.
"Finally, some of the adverts could end up being out of date and misleading if they are left in books for too long."