The polls turned in March which coincided with Corbyn’s response to Salisbury and antisemitism becoming a big issue
October 2018 voting intention polls
October 2017 voting intention polls
Survation’s chart shows the timing of the switch
The Survation chart shows the LAB-CON splits in its Westminster voting intention polling since GE2017 when, of course, the firm was the most accurate pollster. Since then it has generally been recording the best figures for Labour and at times, like at the general election, has been out of line with other pollsters.
As can be seen things were going positively for Labour until late March when its share moved down from the 43%-45% range and has been broadly lower ever since.
There’s a great danger in looking at what was taking place at the time of the downturn and reading too much into it. Correlation is not causation.
However there were two big developments during the latter part of March – his initial response to the Salisbury chemical attack and the row about his positive comments on Facebook about a mural which was said to be antisemitic.
It was the latter that triggered the demonstration outside parliament by members of the Jewish community and their supporters as well, over the month, a series of stories about what the leader had done in the past.
We do know that in the London elections on May 4th the Labour aggregate vote was 43.9% which was way down on the 54.6% of GE2017 and all the polling for May 2018 elections.
My view is that the Salisbury response and the ongoing antisemitism row caused damage to Corbyn and his party from which it has yet to recover.