25/06/2016 04:23 BST | Updated 26/06/2017 06:12 BST

On Thursday, 'Small Town Britain' Roared - Labour Must Prove It Can Win Beyond London and Big Cities

Rob Stothard via Getty Images

Britain is to Leave the European Union and every MP, of all parties, has to make the best of this new path.

The Prime Minister has taken responsibility, as he should, for calling the referendum and for the public rejecting his advice to Remain. Cameron posed as a Euro-sceptic to win the Tory leadership, spent years appeasing his Euro-sceptic right wing, and ended with the reckless gamble of the referendum, becoming a newly converted Europhile for the last three months.

The result is his demise, the UK's departure from Europe's coalition of nations and a risk to the future unity of the UK. This will be Cameron's disastrous legacy.

But Labour needs to be honest about what has happened as well.

Feelings triumphed over facts. The public rejected warnings about Britain being worse off, because they had strong feelings about the impact of immigration.

The benefits of immigration to the UK, the need for migrant workers to fill important jobs in the UK, was lost in this debate. Voters were protesting against a change in their communities they didn't like.

We needed a response that showed understanding; a counter to the politics of hate promoted by too many on the Leave campaign. Their immigration scare stories were, frankly, shameful.

But anyone who suggests the Leave voters did not have this concern upper most, bolstered by an anti-politics mood - is sidestepping the truth.

This was as much a slap in the face for Labour as for the Government.

Labour needs a frank debate about that failure; the break between Labour's united view that the UK should Remain; and the feelings of large numbers of our voters.

Traditional working class Labour voters need to see that Jeremy Corbyn understands their concerns over immigration and will do something about them.

I campaigned with Jeremy in Doncaster, put his message on our newsletters, organised a business Q&A with Alan Johnson, gave my support to national campaign days and door-knocked regularly since January.

This campaign reminded me that message is everything. Leave had a simple message: "take back control"; however, dishonest. Jeremy chose to argue a different message from Cameron, the SNP or Plaid Cymru. His message that the EU needs lots of reform and we need to fight from the inside to achieve it, was too subtle and too complicated, when the heart of this question was always: 'is the EU we have today good or bad for Britain?'

Voters were not deciding the merits of a new, improved EU of the future. They were judging the here and now. Many felt the UK had no control over immigration and wanted to make clear their anger and rejection of that.

A few months ago, Labour expected that it would persuade 70-80% of Labour voters to back Remain.

Sadly, we failed to get that message over early enough.

Just a few weeks before the vote, half of our voters did not know that Labour was saying 'Vote Remain'. The Leave campaign's added to the confusion with their red bus, red posters, and NHS message.

In the end our supporters have split down the middle. I want to hear Jeremy and the Shadow Cabinet, give an honest assessment of why Labour failed to persuade them.

This campaign proved it is not enough to win support in London and the big cities - the heart of Jeremy's support. On Thursday, small town Britain roared. The voices of towns in former industrial, coastal and rural areas across England and Wales, who feel left behind, was heard loud and clear. And large swathes of Labour voters among them.

This vote opened a chasm between our voters and the Labour Party in too many parts of our heartlands. We will need to repair it. The uncomfortable truth must be faced, or Labour will not rebuild our relationship with many of our longstanding voters.

There can be no glossing over this failure. I don't want spin or nonsense about "people kicking the Government" and "austerity". Austerity was hardly mentioned. Immigration was raised more than any other issue.

During the post-mortem, Labour MPs, MEPs, councillors and members will have to decide whether Jeremy can reassure and re-unite our supporters beyond London and the major cities. And do so, before a possible autumn general election against a new Tory leader.

This referendum was the most important campaign Jeremy has undertaken since he became Leader. He must share responsibility for this defeat. On the evidence of this campaign, Jeremy has not demonstrated the strength and presence to rebuild that support. Without it, we cannot hope to carry the country and win a general election.

The many members who worked so hard in the run up to 23 June deserve no less. And none want Labour to face a third general election defeat.

Caroline Flint is the Labour MP for Don Valley