Bunter - any grossly overweight youth. From a fictional Schoolboy, Billy Bunter (see picture below)
Claggy - wet and uncomfortable, referring to clothes.
King Dicky - a bricklayer. Rhyming slang: King Dickie = Brickie = Bricklayer (not what you were thinking).
Gobslutch - a person with disgusting or filthy personal habits.
Early door - a prostitute. Rhyming slang: Early door = whore = prostitute.
Nadgers - small problems or difficulties (always plural).
Palsy-walsy - excessively friendly. As in 'she's a bit palsy-walsy, isn't she?
Rattle and clank - a bank. Rhyming slang.
Day after the fair - when it's too late. As in 'thanks for showing up, but you're a bit day after the fair'.
Booed and hissed - intoxicated due to drink. Rhyming slang: Booed and hissed = pissed = drunk.
Doodad - someone or something for which the correct name has been forgotten.
Spud-grinder - the gullet. As in 'Ooh, that was a punch to the spud-grinder'.
Three-piece suite - the male sexual organ. That's pretty self explanatory.
Unmentionables - underwear. Said Vera Duckworth or Les Dawson-ish.
Housemaid's knee - the sea. Rhyming slang. Like it, but couldn't find the derivation.
House of Lords - a men's toilet. Possibly from: Lords and Ladies, Ladies and Gents....
Creaking gate - an invalid who neither recovers nor gets worse.
Alf's peed again - Be seeing you. From the German 'auf wiedersehen.' That's funny.
Splash the boots - to urinate.
Raquel Welch - a belch. Rhyming Slang. As in 'oops, 'scuse me - that was just a Raquel' (see picture below).
Max someone - to confuse someone. As in 'this test has maxed me out.'
Ice cream - man. Rhyming slang: Ice cream (freezer) = geezer = man.
Happy as Larry - carefree, very happy. Not sure who Larry was.
Ground bones - powdered milk.
Giggle factory - lunatic asylum. That's a bit harsh, but you get the picture.
Mow the lawn - to shave with an electric razor.
Half a nicker - vicar. Rhyming slang.
Set the Thames on fire - to make a great success in life, etc. As in 'not sure if England will set the Thames on fire at the World Cup.'
Uppers and downers - the teeth...inside the north and south, mouth.
Turnip-basher - a rustic individual, a country bumpkin (but not us folks from Devon).
and lastly a Lionel Blair - a chair, or a Lionel Blair-cut - a disastrous hair cut. Obviously (and there he is below).
British Slang and Colloquial Expressions
Part 1 (I know we'll do more of these): Here's a bunch of the oddest ones that you may or may not have come across, but that you should definitely start using again...