My good friend Jonathan Thomas of Anglotopia.net has put together a cute compendium of "British Slang from A to Zed". It's a slight, self-published tome and by no means exhaustive, but if you are, as Thomas says, a "viewer of British TV" and you have ever been stumped by a Scottish character saying "Wheeshd!" or "We're the quality polis!" or maybe you have no idea what a "bacon butty" or a "chancer" is. Or perhaps you're terribly confused when someone says "I'll just get my Macintosh" and instead of reaching for their Apple computer product, they grab a...jacket?
Thomas's dictionary explains those puzzling phrases and words that State-Side British-fans like us may want to brush up on before we sit down to watch a miniseries set in Wessex or even going on our own trip across the pond. It's split up into six categories of British slang (London, Cockney, Scottish, West Country, Yorkshire and Scouse) apart from the larger general dictionary and there's Australian slang and recognizable British insults thrown in for good measure.
Given its slender size and its emphasis on more recent pop culture linguistics in the U.K., this is more of a lighthearted look at British English, rather than an OED-sanctioned official reference, but that doesn't discount its usefulness. Especially if you're an Anglophile newbie or are too bashful to ask a native "Pardon me, but what exactly is a 'treacle'?" but yet you still burn with curiosity to know the truth, this will honestly be very helpful to you. There's even a British Slang Submission Form in the back so that the experts among us can let Thomas know what he needs to include for the next edition.
So, in sum, you need to buy this. Like right now. Do it! You can also read more and order the book directly at www.britishslangdictionary.net
As a companion piece to Thomas's book, I recommend another dictionary of sorts from The National Trust in England: "More Tea, Vicar? An Embarrassment of Domestic Catchphrases" is a compilation of nostalgic, cheeky sayings going back to the 19th century in Britain. Some were submitted by everyday folks who remember what their great aunt Florence used to say when all was said and done: "Everybody to their liking, as the old lady said when she kissed the cow." (page 58) ...Err, what? Cheeky and quirky, indeed.
Put the two books together and you'll have a nice combination of new and old British catchphrases/slang. It will take the mystery and head-scratching out of watching British television and film forever.