For the second year running, the bestselling author's books are the most-donated to the charity shop chain

Dan Brown has hung on to the dubious honour of being the author whose books readers most want to get rid of, topping the list of writers most-donated to Oxfam shops for the second year running.

The bestselling American author, whose latest cryptographic thriller The Lost Symbol – filled with such gems as "Is there life after death? Do humans have souls? Incredibly, Katherine had answered all of these questions and more" – was published last autumn, is joined on Oxfam's most-donated line-up by the likes of John Grisham, Patricia Cornwell and Alexander McCall Smith.

The rants of Jeremy Clarkson, meanwhile, have made the Top Gear presenter the first non-fiction writer to enter the charity's top 10 of authors most likely to be donated to its 686 shops: either his readers are notably generous, or unwilling to keep his titles on their shelves once read.

"Although we do have books given to us which people have had on their shelves for years – classic literature and collectible items – we also have books which are very current," said Sarah Farquhar, Oxfam's head of retail operations. "Jeremy Clarkson is someone people want to read about – he's one of those love/hate figures. When people read him they pass him on – books don't depreciate in value because they've been read."

Ian Rankin crept into the most-donated list just behind Brown, but the Scottish crime novelist is unlikely to be too downcast by his readers' propensity to give his books away: his novels about the exploits of detective John Rebus have also made him the charity's bestselling author for the second year in a row, followed by new entries Stieg Larsson and JK Rowling.

"It's great to be Oxfam's most purchased author for the second year in a row - and I'm really pleased that readers are donating my books to Oxfam, too," said Rankin. "The terrible scenes from Pakistan and wmoest Africa on our TV screens at the moment make it clear how vital the work of organisations such as Oxfam is, and I'm really glad that my books are going some way to help with this."

But Farquhar said that although book sales at the charity were up by around 6% this summer compared with last, the quantity of books being donated to shops had fallen by around 15% over the same period.

"We are struggling with donations. Generally we do find in times of austerity that people don't have quite so much to give," she said. "It's our biggest problem. We're not struggling for people to sell to, but shops are saying they could do with more product. We are consistently hearing that the volume of books donated is down."

Pointing to the fact that the average selling price for a book in an Oxfam shop is £1.60 – the sale of four books would be enough to provide six health check-ups in India – Farquhar urged people to keep on giving. "We need to encourage people to continue to donate to us," she said. "We really value their donations."

Oxfam is the third-biggest bookseller in the UK, and Europe's biggest high street retailer of second-hand books.

The most donated authors to Oxfam shops are (with last year's position in brackets):

1. Dan Brown (1)

2. Ian Rankin (3)

3. Patricia Cornwell (9)

4. Alexander McCall Smith (New entry)

5. John Grisham (2)

6. Danielle Steel (4)

7. JK Rowling (7)

8. Jeremy Clarkson (New entry)

9. Maeve Binchy (New entry)

10. Bill Bryson (New entry)

The Oxfam shop bestseller list (with last year's position in brackets):

1. Ian Rankin (1)

2. Stieg Larsson (New entry)

3. JK Rowling (New entry)

4. Stephenie Meyer (4)

5. John Grisham (New entry)

6. Patricia Cornwell (New entry)

7. James Patterson (9)

8. Terry Pratchett (5)

9. Kate Atkinson (New entry)

10. Dan Brown (2)