Phil Collins said "wanker", not "plonker": "You must take me for a right wanker!". He talked about in an interview before the episode was screened over here. He asked the production people if they knew what it meant (wank = masturbate, if you don't know), and they said, no - it's some kind of term of opprobrium in England, isn't it? I watched the series dilligently until he said it, then I stopped watching. Not used in polite circles here (not yet!).

How about these:
as much use as a chocolate tea pot
as queer (gay, tht is) as a chocolate frog
as queer as a nine-bob note (WRT the old ten-shilling [50p] note)
And finally, a humorous little number using the last above: "Did you know Pavarotti, Domingo and [what's-his-name] have made a record with Julian Clary? It's called Three tenors and a nine-bob note!"

Just remembered this: my mmother used to tell us of for calling the canal the "cut" (there's about 200 miles of canals where I come from). Years later, I found out it's called the cut because that's what the engineers who designed canals called them. Now I get my own back by pulling her up over "who" and "whom", and "can't hardly".

Steve