Book shops are offering aggressive discounts on their bestsellers in the run-up to Christmas in a "cut-throat" price war.

The stores usually try to restrict discounting to slower-selling books, keeping chart-toppers at the full price, particularly in the peak month of December.

But this year they have been forced by competition from supermarkets to slash prices of their most popular titles.

Nicholas Clee, editor of The Bookseller magazine, said: "Discounting has become more intense because of cutthroat competition on the high street. The supermarkets started it but chains like Waterstone's and Ottakar's have to follow them - nobody wants to be undercut."

Waterstone's set a new benchmark last week with a half-price deal on its top seller, Bill Bryson's A Short History Of Nearly Everything, which was on offer for a week at £10 - half its recommended price.

Mr Clee said the price war was driving the cost of new books down to historically low levels. Until the abolition of the net book agreement in 1995, no discounting was allowed. Since then, prices have fallen year on year.

Latest data suggests that the average price of a new book sold in Britain in the last week of November was £7.86, down from £8.02 in the same week last year.

Although the discounting is biting into profit margins, it has provided a huge boost to sales. Last year's surprise Christmas winner was Trinny Woodall and Susannah Constantine's What Not To Wear, which sold by the tens of thousands after Waterstone's dropped its price.

The most striking feature of this year's Christmas rush is the success of quirky books such as Eats, Shoots And Leaves: The Zero Tolerance Approach To Punctuation by journalist Lynne Truss.

Another huge seller has been Idler magazine's 50 Crap Towns, a guide to Britain's most depressing places to live.

The best-selling cookery book is Paul Hartley's Marmite Cookbook, a collection of 70 recipes based on the famous spread, while the most popular gardening book is Sarah Ford's 50 Ways To Kill A Slug.