Up the pole an' 'alf-way round the flag?

Question

"What do you think o' that one?" asked the inspector of the sergeant when Pender had stumbled out of the station.

"Up the pole an' 'alf-way round the flag, if you ask me," replied his subordinate. "Got one o' them ideez fix what they talk about."

"H'm!" replied the inspector. "Well, we've got his name and address. Better make a note of 'em. He might turn up again. Poisoning people so as they die in their baths, eh? That's a pretty good 'un. Wonderful how these barmy ones thinks it all out, isn't it?"

I can't figure out the above bold part of the sentence, which is from "The Man Who Knew How" by Dorothy L. Sayers.

Sounds like the policemen regarded the guy (protagonist in the story) as a gaga.

But I am not sure about the exact meaning of 'up the pole and half way round the flag' and 'got one of them ideez fix what they talk about'.

Answer 1

"Up the pole an' 'alf-way round the flag", in more standard writing is "up the pole and half-way around the flag". "Up the pole" is UK slang for insane. The part about being "half-way around the flag" does not appear to be a common phrase, but rather, it serves as an extension of the previous expression and intensifies it.

"Ideez fix" is an intentional misspelling of "idée fixe" -- an "obsession", or an idea that dominates the mind. It is intentionally misspelled, to highlight the informality of the conversation, as well as the speaker's unfamiliarity with the actual phrase.

"What they talk about" is informal and humorous, and can be interpreted as "that they talk about".

So, to summarize, the subordinate thinks that Pender is insane, and has what some people call an idée fixe -- an obsession.