Rhyming slang
Of the various forms of British slang, the best-known is London rhyming slang (often referred to as "Cockney" rhyming slang, after the traditionally cheery inhabitants of the East End of London. More accurately, its use is widespread throughout London and, through cultural appropriation, beyond). Popular television programmes (notably Steptoe and Son, The Sweeney, Minder, Only Fools and Horses and certain broadcast stand-up comedians) have ensured its understanding, adoption and development in the wider UK.
Rhyming slang usually omits the rhyming, second component that connects the expression to its meaning. Obviously, this is a useful ploy for engaging in criminal or other secretive activity, providing those who are meant to be excluded don't know the code, and those who are meant to be included do know it. As an example, the expression "use your loaf" (suggesting that an individual should apply further thought) derives from "loaf of bread", meaning head. Another example, the humorous (or sexist, depending on PoV) use of "trouble" to denote a female spouse: "trouble and strife" = wife.
Adam and Eve: "believe", as in "would you Adam and Eve it?!"
Apples (and pears): "stairs".
Aristotle: "bottle" (see below), often abbreviated, as in "don't just sit on your 'Aris' all day. Go and do something".
Barnet (fair): "hair".
Barney (Rubble): "trouble". Anything from an argument to a fist fight, as in "Ken got into a right Barney with his wife". Obviously derived from the Hannah Barbera character.
Battle cruiser: "boozer", a pub (or public house)
Berk: abbreviation of Berkley hunt, a female anatomical feature used as an insult, though the rhyming slang version is considered not so insulting as its literal counterpart. In use, "don't be a Berk, you can't put your trust in that geezer".
Bird (lime): time, a prison sentence.
Boat (race): face (specifically one's visage). There was a rather sexist pop song in the 1970s which contained the line "Nice legs, shame about the boat race".
Bottle (and glass): arse (London elongated vowel in glass). To have "lost your bottle" is to have become afraid, especially after commencing a hazardous activity.
Brassic: from rhyming slang, "boracic (lint)" which, historically, was a kind of medicated bandage. To be "brassic" is to be without money, or "skint" (skinned), or "potless".
Bristols: from the rhyming slang "Bristol City", derived from the name of a football (US soccer) club. It refers, in plural (Bristol cities), to female anatomical features.
Brown bread: "dead", as in "did you hear Simon's brown bread? He was hit by a bus".
Bubble (and squeak): a Greek person (now thought to be an offensive term). Originally, "bubble and squeak" constitutes the various leftovers from a celebratory meal (often Christmas dinner), fried.
Bull (and cow): a row or strong verbal disagreement.
Bunny: an abbreviation of "bunny rabbit", itself a variant on "rabbit (and pork)", rhyming slang for "talk". It is usually used to denote garrulousness.
Butcher's (hook): "look", as in "let's have a butcher's at your magazine".
China (plate): "mate"/friend, as in the greeting "you alright, me old china?"
Cobblers' (awls): "balls", ie cojones (also bollocks, knackers, etc), as in "don't talk cobblers/bollocks".
Custard (and jelly [US jello]): a television set, often called a "telly" in Britain (though "TV" is also in use), as in "switch on the custard, I want to catch the news and weather".
Daisy roots: "boots".
Dickie (bird): "word", as in "don't say a dickie (bird) to the police, or else..."
Dog (and bone): a phone/telephone, as in "get the guv'nor on the dog, I need to talk to him".
Flowery (dell): prison cell.
Gregory (Peck): "neck" or for a "cheque" (US check, a method of payment), in use either "get that pint (of beer) down your Gregory" or "you can pay me by writing a Gregory" respectively.
Half inch: to "pinch" (steal).
Hampton (Wick): a prick or dick. British radio's Goon Show often used rhyming slang and derivatives to get double entendres passed BBC censors, eg they sometimes referred to a character called "Hugh Jampton" (huge Hampton).
In and out: "snout" (nose).
Jack and Jill: till (US cash register).
Jack (Jones): to be "on your Jack" is being on one's own.
Jacobs' (crackers): nackers (cojones), as in "turn it in or you'll get hoofed (kicked) in the Jacobs". Derived from the name of a popular biscuit for cheese.
Jimmy (Riddle): "tiddle", to urinate, as in "Bob's gone for a Jimmy".
Kettle (and hob): a watch, originally a fob watch (hence the rhyme), but also now applies to wristwatches, as in "what's the time by your kettle?" Kettle is also used to describe the police practice of surrounding and containing crowds. It is also one's posterior: "kettle (drum)" = bum. There's another use, which I still have to research.
La-di-dah: cigar. Can be abbreviated to "Lah-di", and a better example of the use of the phrase "do what?", to show its not always contextual usage, might be as a reply to the suggestion "There may be more to pay", answer "do what?!"
Long in the boat: the facial appearance of being disappointed, "boat race" being rhyming slang for face.
Merchant bank[er]: w*nk or w*nker, an onanist, often used to describe a contemptible person. "Barclays" is similarly associated as "Barclays bank" (a well-known British retail bank), the verb for the noun.
Minces: derived from the rhyming slang "mince pies" = eyes, as in "keep your minces open for the police".
Moby (Dick): jail or "nick".
Moriarty: party.
Mutto n: derived from the rhyming slang "Mutt and Jeff" = deaf.
North and south: "mouth".
Old King Cole: "dole", or State Unemployment Benefit. Equivalent to "national handbag" in Polari slang.
On your Tod (Sloan): to be alone.
Peckham (Rye): a (neck) tie.
Pen and ink: "stink".
Penny stamp: "tramp", a hobo.
Peter (Pan): a can, either a safe to be cracked or a prison cell.
Plates (of meat): feet, as in "I've been working hard. I feel like putting my plates up and having a beer".
Porkies: abbreviated from the rhyming slang, "pork pies" = lies.
Rabbit (and pork): "talk", as in "she's got a lot of rabbit" (she's rather garroulous). Also see "bunny".
Radio Rental: "mental" (insane, stupid or lost control), as in "Roddy went Radio Rental and hit the guy". Derives from the company name of an extinct consumer electronics business.
Rattle (and Clank): a bank.
Reels (of cotton): "rotten", generally used to describe a situation that has turned out badly as in "we tried to straighten the situation out, but it all went reels".
Richard (the third): from the king killed at the end of the War of the Roses, a "bird", or young woman. It might now be considered offensive.
Rosy (Lee): "tea", as in "put the kettle on—let's have a cup of Rosy".
Rub-a-dub: a pub or public house.
Ruby (Murray): deriving from the name of a mid-20th-Century Irish singer who was popular in Britain, Ruby, or Ruby Murray, is rhyming slang for a curry, the Brits being fond of Indian cuisine—"let's have a beer, then go for a Ruby".
Sausage (and mash): cash. Derives from a staple of unsophisticated English cuisine, sausages served with mashed potatoes, onions and (English) gravy.
Sexton (Blake): rhyming slang for "fake", derived from the name of an early 20th Century literary detective adventurer.
Shave (and a shear): "beer".
Sherbet (dab): a (taxi) cab, deriving from the name of widely available confectionery based on a Middle Eastern recipe. But note that "sherbet" can also apply to an alcoholic beverage, especially (a pint of) beer, as in "fancy a sherbet down the battle cruiser/rub-a-dub?"
Shovel (and pick): the "nick", or the jail in a police station.
Syrup (of fig): a wig (hairpiece), as in "Jack looks stupid in that ginger syrup".
'Taters: cold, derived from London rhyming slang "potato mould" where "'taters" is a common abbreviation of "potatoes" while "mould" is obviously a spread of fungal spores. In use, "don't go out without a coat, it's 'taters outside". Also see "parky" and "nippy".
Tea leaf: "thief".
Tod (Sloane): to be "on your Tod" is to be alone.
Tom (Foolery): jewellery (US jewelry).
Two and eight: "state", as in "Barney's girl dumped him and now he's in a right old two and eight".
Vera Philharmonic: hybrid rhyming slang derived from Vera Lynn (a British singer during WWII who famously sang We'll Meet Again, which was used post-war at the closing of Stanley Kubrick's film Doctor Stangelove and the word "Philharmonic", meaning a gin and tonic (water).
Well...: slang replacement for "very", as in "Tom's well Brahms", (Tom's very drunk). "Brahms (and Liszt) is being pissed (drunk). "Mozart" (and "Liszt") is also used in the same context.
Whistle (and flute): "suit". In use, "put on your best whistle, we're going up west" ("up west" is an East London term for the West End of Central London, the main shopping and entertainment area of the Capital).