London Slang tries to focus solely on slang which is currently used in England’s capital. The layout is a little hard on the eyes, but the definitions are good and the list is fairly comprehensive. Particularly amusing is the “just heard” section, which lists new phrases that may or may not catch on. Includes some Cockney rhyming slang. Organized alphabetically
Cockney Rhyming Slang is a guide to the rhyming language spoken in the East End of London. The site translates both English to Cockney and Cockney to English, and includes an amusing “Cockney Alphabet”. Although the site notes that some Cockney terms date back to the 16th century, its definitions fail to include the dates of usage. Organized alphabetically.
Septic’s Companion is a relatively comprehensive dictionary of words which are common in Britain, but unused (or differently defined) in the U.S.. The site is organized both alphabetically and by topic, and the definitions show a good sense of humor.
Dictionary of the Vulgar Tongue is a repository of British underworld slang (”thieves’ cant”) from 1811. Although this book can also be found through Project Gutenburg, the above website provides more accurate transcriptions. Organized alphabetically.
Peevish is an extensive dictionary of UK colloquialisms whose only drawback may be its inclusiveness; some of its terms are very obscure while others are so common that they can barely be considered slang. Organized alphabetically; includes a search engine.