We do not know yet how high a proportion of the British baby boom will be Muslim, but it is certain to be much higher than the 4.8 per cent in the 2011 census. Eastern European  birthrates tend to be lower than in Britain, so it seems likely that the higher fertility of mothers born abroad is largely explained by the Muslim factor. True, the authoritative Pew Forum predicts that Muslims will only reach 8.2 per cent of the UK population by 2030: once here, their fertility declines. But this leaves out of account a third factor, hitherto less significant than immigration and fertility, namely conversion. Long before Muslims achieve majority status in a community, conversion may become advantageous to non-Muslims. While the main driver of conversion today is intermarriage, a proselytising Islam may strive to fill the faith vacuum. Yet the fact that people of all faiths and none suddenly seem to be having children suggests that there is nothing inevitable about an Islamic Europe. Indeed, the next generation of Europeans may be more robust in preserving their civilisation precisely because they will have rediscovered its Judaeo-Christian origins, and hence are less apologetic about its virtues than their elders.

Prophecy is always an inexact science. As Jonathan Sacks, the former Chief Rabbi, argues, following Maimonides, the test of a true prophet is good news, not bad. God often relents and forgives, so that calamities foretold do not in fact happen. If the worst does not occur, it may be that people have heeded the prophet's words and repented. But God never revokes his promises and the true prophet who offers hope will be vindicated. Pope Francis's new encyclical, Lumen Fidei ("the Light of Faith"), is largely the work of his great predecessor, and we can hear Benedict XVI's quietly admonitory voice when he speaks of "a massive amnesia in our contemporary world" which fears fanaticism so much that it rejects any connection between religion and truth. "The question of truth is really a question of memory, deep memory," he writes, "for it deals with something prior to ourselves . . . It is a question about the origin of all that is, in whose light we can glimpse the goal and thus the meaning of our common path." 

That deep memory is perpetuated when each generation passes it on to posterity. In the phenomenon of birth, our civilisation renews itself. We say: where there is life, there is hope. But the converse is also true: only where there is hope will there also be life.