The vouchers are redeemable in bookshops which choose to participate between World Book Day itself (April 23) and May 4. But there is confusion over whether the word “bookshops” on the voucher applies to school bookshops. Schools which decide to accept the vouchers for books sold in school will only get the money back if their book supplier is taking part in the scheme - and at least one large one has already decided not to.

Books for Students, which supplies around 3,000 school bookshops, will not be handling the vouchers. “The philosophy behind the day is brilliant,” said sales and marketing director David Lindley. “But this is really a high-street promotion designed to increase traffic through retail shops.

“We really can’t ourselves underwrite the enormous costs on top of the discounts and benefits we already give, and we must be careful not to put schools themselves in a position where they will be obliged to bear a loss of Pounds 1 for every book sold.”

Meanwhile some small specialist children’s bookshops, worried about the losses they will incur, may limit their participation.

While publishers, distributors and other sponsors are meeting the cost of printing and distributing the vouchers, the cost of giving each child Pounds 1 discount is being met by booksellers (except in the case of The Children’s Book of Books, priced Pounds 1, which Puffin and Random House are supplying free to shops.) Generally, a book sold at less than Pounds 3.99 means a loss for the smaller bookseller. The deficit will be worst for those who sell a large number of the many other books on the market at Pounds 1 during the voucher period.

Ironically, it is the independent children’s booksellers who already have many child customers and strong links with local schools who stand to make the biggest losses.

Although keen to support World Book Day in principle, some are deciding that the long-term gain of encouraging a new generation of readers may not be worth the short-term pain of a huge loss leader.

Angela McPherson, chair of the Booksellers’ Association children’s group, said: “In theory World Book Day is wonderful,but schools should understand that it is the booksellers who are meeting the cost and it’s a very expensive exercise for those of us who deal with a lot of children. If you’re a small bookshop and you’re the only one in a town with several schools, the impact is enormous.”

She will be accepting vouchers in her shop in Lewes, East Sussex, but is limiting the number of school book fairs she runs in the fortnight around the day. She is also lobbying publishers to ask for more help in underwriting the voucher offer.

Sonia Benster, owner of The Children’s Bookshop in Huddersfield and a member of the BA council, said she was prepared to make short-term losses “because to introduce a child to the experience of book-buying is an extremely valuable thing.

“But after 25 years in business, I am better able to bear the losses than other small children’s bookshops.”

The ideal, she said, was that the vouchers should encourage parents to take their children to bookshops. Schools who wanted to take groups of children to spend their vouchers in shops should book in advance.