Almost constant social drinking.
A character is always smoking tobacco from a pipe.
People are implied to be on harder substances but drug use is never shown. One scene shows a weed plant and implies cookies are edibles in one episode. A weed plant is shown in the same episode.
In one scene a room is full of smoke implying weed has been smoked.
A character has an operation to have his foot removed for years of smoking cigarettes.
Some smoking of cigarettes in earlier seasons.
In one season, two characters enter a room filled with cigars and pipes. One of the characters tries seven brands of tobacco and emerges from the shop surrounded by smoke.
The character Pete 'The Jakey' MacCornack is an alcoholic. Despite this, he's only ever seen intoxicated once. The character is replaced in later seasons, due to the death of the characters actor, and is replaced by a heroin addict called 'Methadone' Mick. However, Mick is never seen taking any drugs and it's implied that he's become clean.
One of the main locations is set in a local pub. Naturally, alcohol is seen being consumed.
Occasional mild, to moderate drug references.