I have a Lilian/Lily, called after her very working class grandmother, so I do challenge the idea that Jack/Lily are particularly working class, but it is slightly strange how they have become so popular and stayed that way for quite so long.
My dd is 13, so not in the current batch, but we have still met a few. She uses Lilian at school which is much more unusual. ds has a name that became super popular a couple of years after he was born (I think it's also been top ten for ten years), but where we live now it's so unusual that it's frequently misspelled.