Well, now there is a debate on the Moorcock message board. The first suggestion was that I'd discovered a typo, and the phrase was taken from a German expression akin to "every pot has its lid", but we've now confirmed that the phrase as I recounted it appears in various publications of the short story, so it's looking more and more like it wasn't a typo, after all. Instead, the Moorcock board is now wondering if the phrase is a bit of rhyming slang of lid = kid, with pop (not rhyming, of course) = father. My own musing wondered whether there was a drug use reference, given the prevalence of "pop" and "lid" in illicit drug culture.

I'm crossing my fingers and hoping that MM himself will answer.