Actually I think the polls were accurate in this case.
They showed it to be razor close with most analysts figuring large turnout would favor Brexit which is what happened.
For an anomaly one needs to look no further than the recent primary in CA. There Bernie was significantly ahead but he got pounded.
What happened?
Fraud.
Which should give Trump and everyone else some concerns about the upcoming election.
Some of the polls did show it to be close, but even the closest only had the thing tied. The furthest out picked stay by 6.6—a miss of over ten points. The average miss was 7 points—I don’t think that turnout alone explains it.