Here's the first evidence Russia used Twitter to influence Brexit

Russian interference in Brexit through targeted social media propaganda can be revealed for the first time. A cache of posts from 2016, seen by WIRED, shows how a coordinated network of Russian-based Twitter accounts spread racial hatred in an attempt to disrupt politics in the UK and Europe.
Interesting, enthralling, complicate and sensational ... 
                                                    ... until you get down to paragraph 14(!):

Surprisingly, all the posts around Brexit in this small snapshot were posted after the June vote.
"Russian-based Twitter accounts" influenced the Brexit vote in the UK by tweeting affirmative AFTER the vote happened.