He took the stones from Chesil beach in Dorset, the locale which inspired his latest novel of the same name, so that he could keep them on his writing desk for inspiration.
When he announced as much in a radio interview, he created a furor among conservationists and was threatened with a £2,000 fine!
That the pebbles of Chesil are infinitely nickable is explained by Simon Mills. And I greatly sympathize, being a persistent purloiner of beach artifacts myself. Surely the fact that the stones are required for the higher service of art should placate the council officials? (And imagine what McEwan could have sold them for on e-bay once the book hit the Booker longlist!)
Am so mad keen to read On Chesil Beach that I've been studiously avoiding all the reviews of the book and the interviews with McEwan on various literary pages because I don't want any spoilers.
I bookmark then for future returning to this interview by Boyd Tonkin in the Independent, John Freeman's article in the Australian, and Natasha Walters review in the Guardian.
But I might just read the first chapter online ...
(Pictures of Chesil beach taken from here.)