Of the 9.3m people who voted Labour in the 2015 general election, just under 40% - nearly 3.5m of them – voted Leave in the June 2016 EU referendum. Although it was official Labour policy to support Remain, 70% of the parliamentary seats held by Labour – and a much higher proportion if London and some other metropolitan areas are excluded – had Leave majorities. How did this happen? How did not only Labour MPs but also the Party as a whole get so much out of kilter with so many of its supporters?