I am reading Cocaine Blues, the first of the Phryne Fisher Mystery books, and early in the book she is asked to go to Australia to investigate a problem. She agrees, so long as she does it her own pace. “Don’t follow me with cables or the whole thing will be U.P.”
What does “U.P.” mean in this context? I assume it is British slang of the period, but haven’t been able to find any explanation so far.