Google will pay to digitize the books, which are no longer covered by copyright restrictions. They will be available on the British Library and Google Books websites.

Peter Barron, Google’s European spokesman, declined to say how much the project would cost, beyond describing it as “a substantial sum.”

Google has digitized 13 million books in similar deals with more than 40 libraries around the world. But its plan to put millions of copyrighted titles online has been opposed by the publishing industry and is the subject of a legal battle in the United States.

Barron said the company’s goal “is to make as wide a range of items as possible” available online.

“Having richer content means people around the world are searching more for it, and that is good for our business,” he said.

Last year, the British Library announced plans to digitize up to 40 million pages of newspapers dating back three-and-a-half centuries, and it recently made thousands of 19th-century books digitized in a deal with Microsoft available as an app for iPhone and iPad devices.