Quite good < Really good == Very good
You'll often hear something like "I had a nice meal". To me, this sounds like it was just ok, but this actually means the meal was very good. Intonation has a lot to do with it of course; "It wasn't very nice" can actually mean it was really bad.
Taking the piss = giving someone a hard time; "He was really taking the piss."
Whilst == While
Anywhere we'd end a word with "ize", it is spelled "ise". Organise, Apologise
Most words with the "er" sound that we'd spell with "or" is spelled "our", like Colour, Favourite, Behaviour, Neighbourhood, Savour. (This originates from French words and spelling.)
They switch "er" to "re" at the end of a lot of words. I'm not sure if this is a rule, or something that is just often the case. Centre, Theatre, Litre. Metre
They also replace "ice" with "ise" in many places: Practise
The harder it is to understand someone chances are they are from further north in England. When it becomes almost impossible to understand them, it means they are Scottish or Welsh.
Rent is usually listed per week (in London, but not outside). The standard formula for calculating monthly rent is
(Rent Per Week * 52) / 12 = Monthly Rent
When moving into your fist place, expect to pay a deposit of at least 6 weeks plus the first months' rent. :(
Flats often do not have dryers. Be prepared. You will need to get an airer that you can hang your clothes on. Your clothes will take 1 to 2 days to dry on this contraption.
Dates are always Day Month Year
When telling time, "Half n" = "n:30", so: Half 11 = 11:30
Traffic lights: When they are about to turn to green, it will be Red and Yellow at the same time, then green
Electrical equipment uses 240v as opposed to 110v in the US. Most of your electrical equipment will be rated up to 240, but it's a good idea to check before plugging it in
To convert Celsius to Fahrenheit: n°C * 1.8 + 32 = n°F (A handy, and easy to remember shortcut is every 5°C = 9°F)