It'd have to be something reasonably serious for 3 plain-clothed coppers
to break their cover. It wouldn't just be a case of saying the wrong thing (unless it was a murder confession or an offer to sell drugs)
(Johnny Catfish is tee are oh you beebeebee ell ee, Sat 10 May 2008, 0:58, archived)

it was more the fact that there were 3 of them
standing in the middle of a group of post-work drinkers that worried me at all...

i've been offered drugs in soho many a time but i felt a bit meh thinking that the old bill could be standing around listening to my conversations when i'm mouthing off at the pub...
( BluerThanABlueThing is a danger to himself and on occassion shipping, Sat 10 May 2008, 1:03, archived)

Why should what you say change whether you're being overheard by a copper or not?
Loudly laying claim to illegal or questionable acts in a very public place is a deeply stupid thing to do and it's the sign of a bit of a mouthy arsehole, normally.
(Johnny Catfish is tee are oh you beebeebee ell ee, Sat 10 May 2008, 1:11, archived)