What nationality is punk?

I’ve been thinking how much longer things used to take to spread from one country to another. By the time I heard of punk I expect it had pretty much crashed and burned in London but it was still reverberating in other places. My story in this Punk Fiction book is set in Germany and the music is from America and Ireland. So when I saw a union jack on the front cover, I was a bit surprised. Seeing it on my blog looks kind of strange, too.