Even though J.G. Ballard didn't really wanted his archives preserved, even to the point of lying about their existence, he didn't have the heart to destroy them himself.
He could have used some advice from Kafka and Nabakov. Should have burned it all.
The Independent has an article and a video. Also, I love how they describe the loose sheets of paper, showing a level of revision that becomes a kind of visual art:
One of the most remarkable things about the manuscripts for his novels, added Mr Andrews, was the level of revision to his writing. "There was very full evidence that he did a lot of reworking and Tippexing. The first draft was predominantly handwritten and then he would type up these pages, which have been thoroughly revised. Some of these individual pages are works of art in themselves; you see a determination and a violence in the way things have been accrued…. The cutting down and corrections, it was furious. Everything had to be hacked off, everything had to be worked out," he said.
That's something we really won't see in the future, where Word documents often don't have history as such (I believe that's a point made by Wendell Berry, in his essay "Feminism, the Body, and the Machine.")