Stephen Fry and Ruby Wax have backed Oxfam’s appeal for the public to donate half a million books as the charity reports dwindling shop stock.

Both comedians attended a Jubilee tea party at Hay Festival on Monday to launch the appeal for an extra 500,000 books to be donated to the charity which will then sell the books in its shops. The appeal will run until 21 June and members of the public can donate at any Oxfam store.

Festival-goers in Hay-on-Wye are being offered tickets to speaker events in return for donating a bag of books to the Oxfam shop at the festival.

Oxfam’s director of trading Andrew Horton said: “Our shops are reporting that stock levels and book donations this year are down, and we need your help so we can continue to raise money selling books across the UK.”

He predicted that if the target of 500,000 book donations is met, the charity may raise more than £1m, which is enough money to support its work in Rwanda for one year.

Stephen Fry said: “It’s really important to look at your bookshelves and find some books that you think you can live without to donate to Oxfam. Books are a wonderful gift because you’re giving something that is brim-full of ideas and stories while also supporting the valuable work that Oxfam is doing around the world. Apart from anything else you’ll clear your shelves for more books!”

Oxfam has 148 bookshops and sells books in most of its 685 shops. In July the charity is hosting the fourth annual Oxfam Bookfest with book-related events set to take place in its shops across the UK.