In 1945, Europe was all but dead, crucified by war and riven in two.  But by as early as 1950, the western part of it was back on its feet: a “European Lazarus”, as Paul Johnson called it.  An economic revival was being driven by new manufacturing – the “Pininfarina car-bodies, Necchi sewing-machines and Olivetti typewriters” that he cites, for example.  This provided jobs for men and a “family wage”, which in turn meant large families and relatively low immigration.  (In 1950, European families were producing 2.6 children each on average.)

By contrast, many of western Europe’s political leaders were old men: Churchill, Adenaeur, de Gasperi.  The revival which they helped to lead looked back to the future – to the Christianity on which European civilisation had been built.  Naziism and fascism were replaced by Christian Democracy.  Although a European coal and steel community was near, the continent was made up of nation states.  Within a few decades, many of Europe’s citizens would be wealthy enough to go on holiday outside their own country, and indeed outside Europe altogether – to Tunisia, for example.

Today, Lazarus is sick again.  Europe has not been reproducing at replacement levels since the mid-1970s.  Last year, one in five Western Europeans was 65 years old or older. By 2030, this proportion will have risen to one in four.  An ageing continent thus needs to work longer to keep up its living standards or else bring in younger immigrants to fund them.  By and large, it has plumped for the second option, and there is no shortage of people who want to come.  Gangmasters round them up on the shores of North Africa.  In the Mediterranean, boats taking them sink.  Italy is overwhelmed.

In this story is to be found the link between the horror on the beach in Tunisia – with the largest loss of British life in a terror attack since 7/7 – and the referendum to take place in Greece, with its implications for the Euro.  When economies age, some immigration is necessary.  One of its upsides is more growth.  One of its downsides is new problems.  Islamist extremism is among Britain’s Muslims.  Most of them reject it, but too many do not.  And when economies age, people want to cling to what they are used to – in Greece’s case, retirement at 61, or 58 in the case of civil servants, on generous pensions.

There is a good case for not turning all Oswald Spengler about this picture of relative decline and, perhaps, fall.  The range of consumer goods now on offer would have dazzled the Europeans of 1950.  As population growth has fallen, sexual freedom has risen.  Doors are open to women that were shut and locked 50 years ago. Europe is arguably returning to an older settlement, in terms of religious practice, rather than embarking on a new adventure: much of Spain and the Balkans was once Muslim.  And here in Britain, we are bucking the trend: birthrates have been rising.

But there are strange repercussions.  For example, there are almost no Muslim state-funded faith schools in Britain.  This is not simply because of a lack of demand by British Muslims, but because of an unwillingness to supply by government.  But a mix of political correctness and good manners means a reluctance to say so.  Instead, there is a flourishing campaign to bar all faith schools – part of the new secularism that has grown since 9/11.  It is striking that Friday’s barbaric murder of a factory owner took place in France, perhaps the most secular country in Europe, and one in which the burka is banned.

Our own response to unprecedented levels of immigration, an ageing population and the terror threat is uncertain.  We ring-fence health and pensions budgets, but raise the retirement age by stealth.  We crack down on bogus colleges and raise English language requirements, but net immigration has risen.  We deploy the language of modern norms – liberal democracy, human rights, equality – against that of the fanatics, but its claims on the individual have less primal power than those pronounced in the name of God or the tribe or the nation.

There are, metaphorically though not literally, age wars.  To younger people, the multicultural society is the norm, free markets are good, same-sex marriage is a matter of equality and rights, Bevan’s National Health Service is a fading memory, and immigration is a good thing, up to a point.  They do not remember a Britain that was more equal and more white.  Older people do.  For many of them, the transformation of the country they live in has been at best unsettling and at worst agonising – bringing with it a profound sense of loss and bereavement.

Very soon, the bodies will be flown home from Tunisia.  Survivors will tell heartbreaking stories, relatives will grieve and weep, and flowers will be piled high at funerals.  Elsewhere, Greece may tumble out of the Euro.  The politicians will turn solemn – declaring that “we will never bow to terror” and that “the European dream will never die”.  Perhaps they are right.  Our values may be less resonant than those of the extremists, but democracy proved stronger than totalitarianism 70 years ago, and may do so once again.

None the less, the stark fact remains: our civilisation is not reproducing itself – at least, in terms familiar to Europeans until very recently.  The ideal of Europe – not of a federal union of states, but of a self-confident powerhouse of culture – has a questionmark against it.  David Cameron and Angela Merkel and Matteo Renzi are wise not to talk in these terms: better to keep things bright, breezy and bouncy.  But the successors of De Gasperi and Adenaeur and Churchill are not powerless.  Consider Cameron’s EU renegotiation package. Parts of his party want it to be much bigger – to be “fundamental”.

But if you think about it, even this demand represents a failure of imagination.  A lesson of Greece is that the Eurozone should go one way – towards complete political and economic union – and countries unsuited to it towards another: a looser relationship with single market access.  Were Cameron’s European strategy to be a truly ambitious one, he would be making a continent-wide case for this end, using all the “soft power” at his disposal.  However, the coming referendum looks likely to offer a binary choice between staying in or leaving the EU as it stands.

Given that choice, Britain should leave.  Better immigration control would be among the benefits of doing so.  There is much else to be done.  Britain needs more houses, so that younger people can buy and start a family.  It needs to wean itself off quantitative easing, so that it makes sense to save.  It needs to push the retirement age up further, and move resources from the retired to younger people – into education, jobs and apprenticeships.  Above all, it needs to shift its defence spending towards internal security while straining to keep Britain’s Muslims onside.