Is Triangle still used in UK for a prison guard? Here the guards are often called "screws"

"screws" here as well. I haven't heard "Triangle" as a UK prison guard, but it brings back 40 year old memories of a prison (I think)folk song with the line "The old triangle keeps on calling" which I think referred to the metal triangle used to call the prisoners to roll-call and meals and generally rule their day. I am going to have to google. and found (3 cheers for google) http://www.acronet.net/~robokopp/eire/oldtrian.htm
Rod