This is a defining moment for the future, and arguably the survival, of the Labour Party. In the coming months there will be much debate about what went wrong and where next.

In 2005 I produced evidence that Labour had lost 4 million voters since the election in 1997. A substantial part of these missing millions were traditional working class voters. This pattern has continued over the last 10 years.

In a minor tidal wave of what looks like pre planned statements, a group of commentators have argued that what lost the election was a failure to tap into the hopes of “aspirational” voters.

However, there is not a shred of evidence for their argument. The explanations for our defeat are deeper than this simplistic assessment.

The truth is that Labour recovered amongst middle class voters but has suffered a cataclysmic decline among working class voters.

It is possible to scrutinise now the initial voting analysis provided to me by the House of Commons Library.

If we compare the election results for our last election victory in 2005 with the result last Thursday and analyse by social class, a very interesting pattern emerges.

Here are the figures.

2005 2010 2015 AB 28 26 27 C1 32 28 30 C2 40 29 30 DE 48 40 37

It is possible here to see that the proportions of AB and C1 voters who voted Labour in the last three elections has held steady. Indeed Ed Miliband’s leadership led to a mild recovery of these voters between 2010 and 2015, (as it did among the C2 group.)

A full analysis of what happened last Thursday is not yet possible but at least one opinion poll has shown that ‘the election result implied by polling would give the Tories 12.5 m votes and Labour 12.2 million. However, in the event the Tories secured 11.3 million votes and Labour 9.3 million.’ There were almost 3 million Labour identifiers that we failed to mobilise.

Labour’s electoral base last Thursday was by far the most middle class we have secured in our history. A strategy based on a misunderstanding of what is happening in our country will not work. We cannot expect to win an election without reaching out to other layers of the population and equally mobilising those Labour identifiers who didn’t bother to vote.

In the coming leadership election, candidates need therefore first of all honestly to demonstrate that they can develop a three-fold strategy in England (Scotland is a very special case):

Hold on to and indeed increase our middle class vote Reach out to working class voters, and Mobilise Labour identifiers who did not vote Labour.

I will shortly publish further reflections on what we do next. However, the party should not elect a Leader who cannot concretely demonstrate that they can deliver B) above, since they are the largest group of the electorate whose support we have lost.

Those in the PLP with leadership aspirations cannot remain in denial or ignorance of these facts. They do so at their own peril, but more fundamentally fail to understand why the Labour Party exists.