The party leader surveying the ruins of his political career with the heaviest heart should not be David Cameron. After all, the Prime Minister has had some successes of which he can be justly proud.

No, it is Jeremy Corbyn who should hang his head in shame and despair. Whether or not he survives in the short-term as Leader of the Labour Party, the Hard-Left member for Islington North is guilty of a double betrayal — of working-class Labour voters and his own principles — that is likely to be fatal to him, and possibly his party.

For there is no doubt it was disgruntled working-class voters in the North-East, Yorkshire, the West Midlands and South Wales who swung the referendum for Vote Leave. As Nigel Farage correctly said yesterday, it was won by ‘the Old Labour vote’. Without them, we should still be under the heel of Brussels.

It is Jeremy Corbyn who should hang his head in shame and despair. Whether or not he survives in the short-term as Leader of the Labour Party, the Hard-Left member for Islington North is guilty of a double betrayal — of working-class Labour voters and his own principles — that is likely to be fatal to him, and possibly his party

Labour heartlands like Sunderland, pictured, voted overwhelmingly to leave the European Union

And there is also no doubt that the issue above all which drove them to vote in favour of leaving the EU was uncontrolled mass immigration. Ignored or patronised for years by major politicians of all parties, they finally expressed their exasperation in the only way they could.

If he had been true to his life-long principles, Jeremy Corbyn would have put himself at the head of this huge army of unhappy voters. Probably the over-riding belief of his entire political career has been a deep antipathy towards the EU.

As a young politician, he campaigned during the 1975 referendum to leave what was then called the Common Market. He worshipped Tony Benn, who was one of the two or three leading lights in the movement to pull out. Benn was his political mentor.

When, after losing the 1987 election, most of the parliamentary Labour Party began to drop its opposition to the Common Market, Corbyn remained an unregenerate critic of the organisation. In 1993 he spoke out against the Maastricht Treaty, which established the European Union and laid the foundations for economic and political union.

Indeed, what he said about monetary union was uncannily prescient. He rightly predicted that it would ‘take away from national parliaments the power to set economic policy, and hand it over to an unelected set of bankers who will impose the economic policies of price stability, deflation and high unemployment throughout the European Community’.

In 2008, Corbyn stood by his principles when he voted against the Lisbon Treaty. He wrote that the EU had ‘always suffered a serious democratic deficit’.

As a young politician, he campaigned in 1975 to leave what was then called the Common Market

Even during last year’s leadership campaign, Corbyn made several anti-EU remarks which set him apart from his pro-EU rivals. During one trade union hustings he said: ‘I would advocate a No vote if we are going to get an imposition of free market policies across Europe.’

Yet after being elected by an overwhelming majority, he soon lost the power of his convictions. Under pressure from pro-EU Labour MPs, he agreed to recommend staying in the EU. This was done in the most half-hearted manner, thereby earning the contempt of both sides.

So it was that the Labour leader idiotically stated during a Sky News Q&A in the course of the campaign that he was hoping to vote for Remain but this was ‘not unconditional by any means’. Such equivocation infuriated almost everybody.

Imagine what his idol Tony Benn would have done in these circumstances. He would have remained true to his principles.

But Corbyn, despite having achieved an impregnable mandate, jettisoned the beliefs of many years. The one-time revolutionary, who had confidently declaimed his opposition to the EU when he was a nobody, became, as Leader, a timid and wholly unconvincing proponent of Remain.

Of course, he was never going to convince most of the Shadow Cabinet to join him in the cause of leaving the EU. But his power in the party was so great that he could have led a Leave faction without fear of challenge.

If he had done that, he would have won the admiration and support of the great multitude of alienated Labour voters in places such as Sunderland, Swansea and Hartlepool who have felt so let done by the party of Tony Blair, Gordon Brown and Ed Miliband.

Yet after being elected by an overwhelming majority, he soon lost the power of his convictions

The reason he failed to do so was not simply a kind of bumbling cowardice. Ensconced in his Islington redoubt, he is surrounded by metropolitan lefties such as his neo-Stalinist director of strategy, the former Guardian journalist and Winchester College-educated Seumas Milne, who neither know nor care about Labour’s working-class voters.

Corbyn is unable to relate to their fears. In his handbook of international socialism, immigration is an unalloyed good which must be promoted at every opportunity. It doesn’t matter to him or to his advisers that millions of Labour voters have seen their wage rates undercut by EU workers, and pressure placed on their schools, hospitals and GP surgeries by uncontrollable EU migration.

I’ve no doubt, too, that Corbyn can’t understand the deep patriotism — and the desire not to be bullied by bloodless Brussels-based Eurocrats — which so many of these decent people feel. His neighbouring Labour MP in Islington, whom he has promoted to be Shadow Defence Secretary notwithstanding her almost total ignorance of her brief, is Emily Thornberry.

Having been sacked from the Shadow Cabinet by Ed Miliband after she had sneeringly tweeted a picture of a family home draped with flags of St George, her banishment did not last long. Corbyn obligingly rehabilitated her soon after his election as Leader.

His almost bone-headed inability to grasp the effects of mass immigration on working-class communities was paraded by him in the most shaming way last Sunday on BBC1’s The Andrew Marr Show.

Having loftily blamed the pressure on housing and schools on the Tory Government’s spending cuts, he asserted with absurd myopia: ‘There is no “uncontrolled immigration”. There is freedom of movement that goes both ways: more than two million British people are living in Europe.’ No wonder Labour supporters voted as they did!

I’ve no doubt, too, that Corbyn can’t understand the deep patriotism — and the desire not to be bullied by bloodless Brussels-based Eurocrats — which so many of these decent people feel

True, Labour’s deputy leader, Tom Watson, appears to have belatedly woken up to the problem. He recently stated that the party would ‘look again’ at the free movement of labour.

But unless the Labour hierarchy wakes up to what is going on, it faces the threat of annihilation in its heartlands at the hands of Ukip such as it has already experienced in Scotland at the hands of the Scottish Nationalists.

If only Jeremy Corbyn had had the courage to identify with Labour supporters by blaming the widely distrusted EU and all its ways, he would stand today as a courageous man who had stuck by his principles. He would, in fact, show he had the moral stature to be prime minister.

Instead of which, this frivolous metropolitan lightweight was seen at breakfast yesterday morning laughing with his aides. He was evidently happy with an outcome for which he was not brave enough to fight.