Hi keberoxu, it's very sad when you have to answer your own question.

We have most of Pratchett's novels but I haven't read them all so I wouldn't have known where to start looking for the crab bucket quote without reading the whole book. I did look at the book (at 2 am this morning when I couldn't sleep) but it would have been a hard, sleepy slog trying to find those little words in a 400 page book.

However, having now read the quote it reminds me of what is known in Australia as Tall poppy syndrome
".

After a quick scan of that article I also found this:

"Usage in Britain

"Prior to becoming British Prime Minister, Margaret Thatcher explained her philosophy to an American audience as "let your poppies grow tall." [16][clarification needed]

"The quote was made in the United States for political purposes and any assertion that the United Kingdom itself has a culture of tall poppy syndrome in the crab mentality sense like Australia and New Zealand[17] has been disputed.[18]"