Fennel, in regard to your post @-18:15 today, it would seem there are many on this forum who state they left the Labour Party on the election of Jeremy Corbyn.
We also seem to be continually hearing of "friends" of forum members who will never vote Labour again due to Corbyn being Party leader.
However, I would remind such persons that when Jeremy Corbyn was elected as leader, the membership of the Labour Party increased by over four hundred thousand.
In the 2017 General Election, the Labour party increased the number of seats it held in the House of Commons and in that deprived the Conservative Party of its overall majority in Parliament.
Sighting local council by-elections or even the European Parliament Elections as any indication of what may happen in a General Election is a very poor pointer I feel, especially in the current ever-changing political situation in Britain.