Arron Banks had a "US strategist"[1] help poll 20,000 people[2], a sample size much larger than YouGov and others[3].

[1] https://twitter.com/Arron_banks/status/746280064652836864

[2] https://twitter.com/Arron_banks/status/745907822194466816

[3] https://ig.ft.com/sites/brexit-polling/