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Twitter co-founder on site's sketchy beginnings

20 June 2014 Last updated at 00:39 BST

It's got more than 250 million users worldwide, including some of the globe's most powerful people - but Twitter had humble beginnings on the back of a scrap of paper.

Its co-founder Biz Stone has written a book about the launch of the micro-messaging site, which has grown into a multi-billion pound business.

He told BBC's Newsnight: "We said lets just work on something that we were interested in. That's all it was. It was just joyful."