Hedge-fund billionaire Robert Mercer offered his data analytics firm's services to the Leave campaign to target voters

A billionaire friend of Nigel Farage and contributor to Trump's campaign fund offered his expertise to help the Leave campaign.

Hedge-fund mogul Robert Mercer co-owns right-wing news organisation Breitbart, as well as data-analytics companies.

His firm, Cambridge Analytica, was paid £4.8 million by the Trump campaign to persuade swing voters to cast their ballot for the property magnate.

He is alleged to have offered his firm's services to Farage for free, according to the Observer.

Mr Mercer also shared his knowledge on how to target voters on Facebook to the Leave campaign.

His work was not mentioned to the electoral commission.

All services worth more than £7,500 should be declared to the independent body.

The US businessman's strategy was to scrape personal data from profiles to learn how their message can be passed around social media networks.

The communications director of Leave.eu, Andy Wigmore, told the Observer: 'They (Cambridge Analytica) were happy to help. Because Nigel is a good friend of the Mercers.

'We shared a lot of information.'

Leave.eu founder Arron Banks also told the Observer: 'AI won it for Leave.'