If you try and immitate English slang in London you will inevitably sound like Dick van Dyke in "Mary Poppins"; that is: excruciatingly embarassing, and make yourself seem like an idiot.
Please just use correct English. Even your own US version will be better than attempting to immitate local slang - and getting it wrong either in meaning or context. In fact, if you get it wrong (especially by inappropriate use) you could cause offence. If you stay long enough then you will pick up the local dialect by osmosis.
For the reason of context you should also avoid using American slang because what may seem inoffensive in a place like New York could be Very Offensive in the UK.
You should also be aware that London is not typical of any other place in the United Kingdom and they sometimes use English in a way which is not common elsewhere (the Dick van Dyke syndrome again). Different speech is used in the different boroughs; even more noticable between the north west and south east of the city.
But if you insist then study some of the many American-English translation sites available on the internet. Ignore the "slang" just stick to the regular language. Then you will be safe and not be risking laughter or a beating.
You can watch Anglophenia on YouTube. It has two or three good videos about the differences between British slang and American slang. It also has several good vedeos about the differences between our cultures.
You can also read *Divided by a Common Language* by Christopher Davies. He talks in some detail about the differences between the two countries and their usages of English.
In addition, @LadyMerton has given a few helpful links.
London is now a multicultural city as you will see when you stand in Oxford street.
All languages are spoken, you will be lucky if there are any native English speakers to talk to.
We speak English
Here are just a few differences:
For a car:
American British
“hood” “bonnet”
“trunk” “boot”
“shift” “change gear”
“gas” “petrol”
“freeway” “motorway”
Others:
“Sidewalk” “Pavement”
“Candy” “Sweets”
“Subway” “Tube” or “Underground”
“Block” No equivalent, simply not used.
“Condominium” “Property”
“Realtor” “Estate Agent”
“Cell phone” “Mobile phone”
“Faucet” “Tap”
Spellings:
“Center” “Centre”
“Meter” “Metre” (as in the distance measurement)
“Favorite” “Favourite”
Many English words ending in “our” have been changed to “or” in America.
Beware of the following:
'Wanker' is not a brand of beer here - it is the equivalent of 'jerkoff'.
To 'knock up' a girl means to get her pregnant, not to call round early at her place.
'Randy' is not a man's nickname here - it is the equivalent of US 'horny'.
'Pants' refers to underwear, not to trousers.
To 'get gas' here implies you are suffering from flatulence - the fuel used by most cars is called 'petrol' here.
Also be aware:
A 'public school' here is an top-rank private school. Publicly-funded schools here are called 'state schools'.
A 'pavement' here is what the USA calls a 'sidewalk'.
There's nothing worse than a foreigner using slang, don't bother. Not even "cheers" or "mate," it's excruciating. Just speak proper English and don't keep saying"in the US we have...." No one cares.
Why bother about slang? Most people speak the same English you do.
Just go with the flow and talk normally..WE in UK understand you and is pretty much the SAME language. We DO use term BLOCK....AND most newcomers speak decent English...
Only thing to avoid is the word fanny. In English this means female genitalia not the buttocks.
