A collection of Narnia books, some signed by the author CS Lewis, yesterday raised thousands of pounds for an Oxford church at a London auction.

The sale of the books would not have been possible without the generosity of Walter Hooper, 77, from North Oxford.

Mr Hooper worked as CS Lewis's private secretary in 1963, shortly before the author's death.

And ever since, he has worked tirelessly to keep the memory of "Jack" alive.

Mr Hooper has written numerous books on Lewis, including the authorised biography with Roger Lancelyn Green, and the three-volume Collected Letters.

Volume III: Narnia, Cambridge, and Joy, 1950-1963, was published two years ago, and Mr Hooper is already contemplating a new "best of" collection, featuring about 1,000 letters in one volume.

The custodian of Lewis's work told The Guide that the big screen versions of The Lion, The Witch and The Wardrobe, and Prince Caspian which is out now, had meant a huge resurgence of interest in Lewis's work over the past few years.

He added: "I get lots of phone calls about Lewis because the films have made lots of people take an interest in his work again.

"Young people will read the Narnia books and as they get older they might take an interest in Lewis's letters.

"Lewis was a wonderful letter writer and felt a responsibility to reply to everyone.

"I was so tired by the time I came to edit the third volume that I said 'Jack, I have spent more time editing your letters than you spent writing them'.

"It was a huge privilege to be able to do it, and in some ways I have continued to be his secretary.

"Harper Collins are concentrating on books linked to the films at the moment, and the film of The Voyage of the Dawn Treader is expected to come out in May, 2009."

Mr Hooper hoped his generous donation will raise thousands of pounds for the Oxford Oratory church in Woodstock Road, which is being renovated.

His collection of 11 books includes three signed first editions and all were expected to fetch about £3,000.

But Mr Hooper is not quite ready to part with all his Lewis memorabilia - he is keeping his treasured copy of the writer's first published work, the poetry volume Spirits in Bondage, which he still draws inspiration from.

He is often in touch with the California-based CS Lewis Foundation, which runs summer schools at The Kilns in Headington, the author's former home.

"The foundation tries to maintain The Kilns as a museum and as a place where people can come and study, and I think they manage it very well," said Mr Hooper.

Although the pensioner no longer owns some of his most prized possessions, he will continue to work on Lewis's letters, with his loyal tabby cat, Blessed Lucy of Narnia, sitting beside him.