24 July 2016 Last updated at 10:07 BST
Speaking to many of the key players in the campaign on both sides, BBC Newsnight's Nicholas Watt tells the inside story of how the Leave campaign won - and how the Remain camp lost this historic vote.
Read more: Cameron considered last-ditch appeal to Merkel
This film aired as part of a Brexit Britain - a special edition of BBC Newsnight one month on from the referendum.
It's one month on from the UK's referendum on EU membership.