A recent survey discovered that of those who thought of voting Labour in 2015 and then did not, the majority turned away because they found the party too centrist and not left enough. This echoes the conclusion of this blog posted months ago.
The same survey found that people voted Tory because they thought Labour useless on the economy. There is a subtle point here often missed. Those who vote regularly out of habit and custom always vote at elections and generally stay close to the centre. However those who vote out of the conviction they want to change things, vote for the left. but they do not vote at all if they are not convinced there is real prospect of change. Thus the SNP victory in Scotland was gained on a much higher turnout that the Tory victory in England.
For Labour to win it must attract not from the centre, but from the non-voting left. In other words if it had attracted back the 5 million votes it lost since the invention of New Labour, it would have had about 14 million in total. The Tories won on a low turnout with just 11 million. The mountain is not impossible to climb if you know which one to go for. 15 million registered voters stayed at home in May 2015.