Though if he grew up in the UK he's more probably the grandchild of those who stayed post-war, rather than those who've arrived post Poland's accession to the EU. Which of course just deepens the story further if he's Jewish.

That's neat: that's an implication I didn't catch, not knowing enough about Polish immigration to the UK. Thank you!

I like the multivalence of not knowing whether Piotr is Jewish or not, but if it was his grandparents who immigrated and were, then two generations is more than enough time for languages and traditions to be dedicatedly lost; for him not to know it himself, perhaps. I know it can happen in less time, but it would match Żaneta's unknowingness of her own grandfather's generation.