Watching David Cameron deliver yet another speech at the JCB headquarters in Staffordshire yesterday, jokes about a man deep in a hole and still digging were hard to avoid.

Where immigration, Ukip, and his turbulent back-benchers are concerned, the shovelling never stops.

The Prime Minister's audience might have forgotten, meanwhile, that the multinational run by his friend (and Tory donor) Lord Bamford has just announced 150 redundancies across its UK operations. JCB has been hit, it reported a month ago, by a "severe decline" in world markets.

These things happen now and then if you operate 22 factories across Asia, North America, South America, and that place known even in Tory shorthand as "Europe". A corporate enterprise has to be nimble, alert to economic fluctuations, and engaged - as is JCB - with the needs of customers in 150 countries.

Anthony Bamford, having given millions of his billions to his party of choice, does not draw the conclusions you might expect. Only in August he was blaming "EU sanctions coming out of Brussels" for damaging his firm's trade with Russia. Mr Cameron - who has found time to open JCB factories in India and Brazil - was not held to account for a Ukraine policy he has supported loudly.

Such is the Tory paradox. "Europe" is a place of allies and opportunities when it suits, but a threat to liberty, sovereignty, trade and the social fabric when eurosceptic fever strikes. Migrants from the east of the EU and their effect on the labour market were troubling Mr Cameron yesterday. So are Poles who work for JCB in Germany stealing our jobs?

The Prime Minister is not interested in subtle distinctions. His only concern over immigrants is that they do not come here. He no longer cares about their lives, their hopes, their needs. Their long-demonstrated contribution to the economy is of no account. The extent to which Britain's public services depend on migrants is forgotten. Mr Cameron has suffered a humiliation thanks to immigration statistics. That, alone, is what matters.

It's not exactly a sound basis for policy. But then, the Prime Minister's "no ifs, no buts" campaign boast to hold net increases in the immigration figures to "tens of thousands" hardly involved Solomon's wisdom. Outbid at every turn by Nigel Farage and Ukip, he lays bigger and bigger bets. Painted into a corner by back-bench Tory sceptics and his own rhetoric, he has another go with the brush.

It won't work, of course. Mr Farage is plain enough: the UK out of Europe, come what may. Mr Cameron's own zealots prefer the language of repatriated sovereignty and "Brussels" humbled, but the upshot is the same. The fantasy is, crudely, that the EU can be dismantled, at the UK's convenience, and the old European Economic Community restored on the UK's terms. Suddenly the model - and this counts as a novelty - is Norway.

The sceptic squadron stands ready to fly in the face of European reality. It forgets that Norwegian access to Europe comes at the cost of obeying EU rules without Norway having any say over those rules. It overlooks the costs incurred by Norwegians for the privilege without any of the economic benefits. Relevant or not, Norwegian net migration numbers are as high as they have ever been. In 2012, almost two thirds of those accepted by Norway were European citizens.

Mr Cameron had 260,000 reasons to speak at the JCB headquarters plant in Rocester yesterday. That was the net migration number in the year to June. It was 78,000 up on last year and it made a mockery of the Prime Minister's promise to get the figure below 100,000 before the 2015 election. Both the totals of EU and non-EU migrants are up. The Government can do something about the latter, if it chooses, but Mr Cameron would rather make an issue of the former. The choice is purely political.

It is dictated, obviously enough, by Ukip and those restive back-benchers. This Prime Minister is not the master of his own destiny. So he winds up giving the wrong answers to the wrong questions, drags the moral cowards of Labour and the Liberal Democrats along behind him, and risks taking the UK out of Europe to save his own political skin. It amounts to a nice morning's work among the big JCB Bob the Builder toys, most of them destined for export.

The old near-racist tropes no longer work. Few still believe seriously that immigrants come here to scrounge from a benefits system hell-bent on victimising the native poor. Equally, token words aside, Mr Cameron does not lead a government capable of admitting that immigration mania flows from a low-wage economy built on insecurity. If you're struggling to survive, the belief that "they're stealing our jobs", or driving down wages, sounds rational. The Prime Minister who allows your misery can't afford to correct the impression.

So migrants must be deterred. No in-work benefits, such as tax credits, for four years. No universal credit. No access to social housing. No child benefit or tax credits for the family some poor migrant has left behind. The trick, for Mr Cameron, is to make sure that none of the native-born get around to asking why anyone has to have wages subsidised in his thriving and expanding - he says - UK economy. The idea is to reduce migrants' earnings to the minimum they might get at home, not remind the British that millions here work hard and remain in poverty.

This proposed selective culling of the poor, one turned against the other, has consequences in terms of EU treaties. The Prime Minister's early efforts simply to suspend the right to free movement have been rebuffed by European leaders, Germany's Angela Merkel not least, so social security might be a better target. Denying one set of citizens the rights enjoyed by others is neither within the spirit nor the letter of European law, however.

So Mr Cameron blusters. He will renegotiate the terms of EU membership with the curbing of immigration as his priority and "rule nothing out" if he does not get his way. "The British people will not understand - frankly I will not understand - if a sensible way through cannot be found, which will help settle this country's place in the EU once and for all," said the bold Brit. He even seems to believe the rest of the EU will happily rewrite treaties.

By no accident, the Prime Minister misses the point. Migrants become scapegoats when governments - or an entire parliamentary system - have failed the people. Those turning to Ukip will be no more prosperous, not by a soiled penny, if Mr Cameron succeeds in persecuting foreign workers. Thanks to his Government's assaults on social security and living standards, indeed, the proud patriots attracted to Mr Farage will continue to struggle.

If the Kippers and the sceptics detach us from the community of European nations things will get very much worse for those Mr Cameron was struggling to placate yesterday. The anti-Europeans feel no need to mention the fact. But Scotland might yet have something to say about the matter.