One kindly soul in Oxford handed in a first edition of the Lord of the Rings trilogy worth nearly £8,000, while in central London a rare 1965 copy of Paddington Bear worth £70 was left on the doorstep.
After decades of being associated with fair trade handicrafts and second-hand suits, Oxfam said yesterday its fastest-growing source of income wassecond-hand books.
The charity said "unprec-edented" demand at its little-known chain of dedicated book stores had prompted plans to increase its number of outlets by up to one quarter in the next 12 months.
Sales at Oxfam's 60 book shops have doubled in the past four years, turning what was once a musty sideline for its trading arm into a multimillion- pound operation.
Last year Oxfam sold 12 million books, raising £13m. This year it expects to sell 15 million, and open 10 to 15 more stores. Book sales account for 25 per cent of Oxfam's annual turnover of £51m from its 700 stores, compared with about 12 per cent in 1999.
Barney Tallack, the charity's strategic business analyst, said: "People are getting back into reading, as we have seen in the new books sector.
"What we have done is get into a position to benefit from that by dedicating staff and stores to turning high-quality donations into something that consumers want. The attraction of browsing in a bookshop is one that does not fade."
The expansion in secondhand sales has coincided with a rapid growth in the new books market, upfrom £2.96bn in 1999 to £3.36bn in 2002. This has led to a windfall for charity stores as readers clear out their bookshelves with increased frequency.
Oxfam claims it has maximised its share of the market by setting up brightly lit and modern stores to get away from the dank and dusty image of second-hand book shops selling dog-eared thrillers and yellowed romances at 20p a time.
The charity says its busiest stores sell up to a thousand books a week. It aims for an average price of about £2 a title and the average annual sales for each store are £170,000.
Oxfam says staff have become practised at spotting valuable classics and first editions. The J R R Tolkien trilogy was sold at auction for £7,900, while staff at the store in Marlow, Buckinghamshire, recently discovered a first edition hardback of Northern Lights by Philip Pullman worth £6,000. The first edition Paddington was found in a box left on the store's doorstep in Marylebone High Street.