@Ali1302, the figures I have seen online for the Cambridge and Oxford endowments are even smaller. More like 2B pounds.
And sure, they can aim for anything. They may even achieve it (though so far, there’s not much evidence that they will reach those numbers any time soon) but keep in mind that the American unis aren’t exactly sitting still either. Northwestern is in the middle of a $3.75B fund-raising campaign. UMich is in the middle of a $4B campaign. MIT is in one as well, though I can’t find the number they hope to reach online; they’re probably in the silent phase now.