Revealed: how US billionaire helped to back Brexit

The US billionaire who helped bankroll Donald Trump's campaign for the presidency played a key role in the campaign for Britain to leave the EU, the Observer has learned. It has emerged that Robert Mercer, a hedge-fund billionaire, who helped to finance the Trump campaign and who was revealed this weekend as one of the owners of the rightwing Breitbart News Network, is a long-time friend of Nigel Farage. He directed his data analytics firm to provide expert advice to the Leave campaign on how to target swing voters via Facebook – a donation of services that was not declared to the electoral commission. Cambridge Analytica, an offshoot of a British company, SCL Group, which has 25 years' experience in military disinformation campaigns and "election management", claims to use cutting-edge technology to build intimate psychometric profiles of voters to find and target their emotional triggers. Trump's team paid the firm more than $6m (£4.8m) to target swing voters, and it has now emerged that Mercer also introduced the firm – in which he has a major stake – to Farage. The communications director of Leave.eu,