If you don’t make your living by refining the internal workings of the European Union, then the recent fantastic interventions of Poland have been extraordinary entertainment – a new branch of diplomacy based on injecting the maximum uncertainty into talks.

To those who want to fashion a more united Europe, the outbursts of the Kaczynski twins, President and Prime Minister of Poland, have been pure distress. Yet for all the wild flailings from Warsaw, there are two serious points behind the Kaczynskis’ position (even if they don’t make those themselves).

First, the 27 members now want very different things from the EU. For all the rush to take in the countries of Central and Eastern Europe, it is not possible blithely to dismiss the legacy of the Second World War and the Iron Curtain, still a vivid memory in the East, even if, in Britain, it is fading.

Second, the financial rewards of joining the union are not what they were for, say, Spain. The new entrants are poorer, and there are more of them. The financial glue that helped buy harmony is weaker. It is not surprising if the newcomers are chippy about their status.

The twins, from the start an indigestible element in EU politics, have caused consternation by saying that they intend to re-open the EU-wide deal concluded bitterly last month. On the face of it, they have nothing to gain; they have already extracted a huge concession from Germany – that new voting rules, which Poland dislikes, will not be phased in until 2014.

But their sense of deep grievance, while out of proportion to any rational cause, does have a small foundation in finance. Poland is paid a lot by the EU; its net benefit in 2005 was €1.9 billion (£1.29 billion), according to the broad-brush calculations in the European Commission budget. But as Simon Tilford, chief economist at the Centre for European Reform, points out, this is less than the figure for Spain (€6 billion) or Portugal (€2.4 billion).

True, Poland will get more when the cap on farm payments to new entrants is lifted (and if anything will make France consider reform of the farm budget, it is the new costs it will then bear). Poland also gets oblique benefits; Poles in Britain sent £1 billion home in April, May and June, say officials, using Bank of England figures. But Poland and other newcomers cannot expect a Spanish metamorphosis.

And the Second World War? The oddest outburst from Jaroslaw Kaczynski, the Prime Minister, was to claim that in EU voting rules, Poland’s population should be taken as 66 million, not 38 million, to allow for losses in the war. But where do you stop? Britain before losing the Empire? Ireland before the potato famine? Or even Germany before the war (about 5.5 million were killed, compared with Poland’s six million). Nor it is clear how he derived the 66 million; officials tentatively suggest he may have included people now in the parts of Ukraine and Belarus which were once Poland, as well as the three million Polish Jews killed in the war. Given old allegations of Polish citizens’ complicity in those deaths, many would contest the propriety of that figure.

But the grievance, preposterously expressed, is a good reminder of the rifts which once tore apart the continent. The EU, whose creation was inspired by the desire to put those conflicts in the past, too often now treats them as taboo in its pursuit of inoffensive cordiality. Even though you can now drink a cappuccino from Prague to Dublin, it does no harm to be reminded of how recently the Iron Curtain fell, and of how, for some countries, even the Second World War seems like the recent past.

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