Follow the data: does a legal document link Brexit campaigns to US billionaire?

We reveal how a confidential legal agreement is at the heart of a web connecting Robert Mercer to Britain's EU referendum

On 18 November 2015, the British press gathered in a hall in Westminster to witness the official launch of Leave.EU. Nigel Farage, the campaign's figurehead, was banished to the back of the room and instead an American political strategist, Gerry Gunster, took centre stage and explained its strategy. "The one thing that I know is data," he said. "Numbers do not lie. I'm going to follow the data."

Eighteen months on, it's this same insight - to follow the data - that is the key to unlocking what really happened behind the scenes of the Leave campaign. On the surface, the two main campaigns, Leave.EU and Vote Leave, hated one other. Their leading lights, Farage and Boris Johnson, were sworn enemies for the duration of the referendum. The two campaigns bitterly refused even to share a platform.