  The recent past has highlighted the influential role of social networks and
online media in shaping public debate on current affairs and political issues.
This paper is focused on studying the role of politically-motivated actors and
their strategies for influencing and manipulating public opinion online:
partisan media, state-backed propaganda, and post-truth politics. In
particular, we present quantitative research on the presence and impact of
these three `Ps' in online Twitter debates in two contexts: (i) the run up to
the UK EU membership referendum (`Brexit'); and (ii) the information operations
of Russia-backed online troll accounts. We first compare the impact of highly
partisan versus mainstream media during the Brexit referendum, specifically
comparing tweets by half a million `leave' and `remain' supporters. Next,
online propaganda strategies are examined, specifically left- and right-wing
troll accounts. Lastly, we study the impact of misleading claims made by the
political leaders of the leave and remain campaigns. This is then compared to
the impact of the Russia-backed partisan media and propaganda accounts during
the referendum. In particular, just two of the many misleading claims made by
politicians during the referendum were found to be cited in 4.6 times more
tweets than the 7,103 tweets related to Russia Today and Sputnik and in 10.2
times more tweets than the 3,200 Brexit-related tweets by the Russian troll
accounts.
