British vs American English

British vs American English: real grammar differences (collective nouns, present perfect, have got), plus common spelling and vocabulary contrasts.

Grammar

Collective nouns: British "Can take a plural verb when the group is thought of as individuals: The team are playing well.", American "Almost always takes a singular verb: The team is playing well."
Recent past actions: British "Prefers the present perfect: I've just eaten. Have you finished yet?", American "Commonly uses the past simple instead: I just ate. Did you finish yet?"
Possession: British "Favors have got: I've got a car. Have you got a pen?", American "Favors have (without got), though have got is understood: I have a car. Do you have a pen?"
Past participle of get: British "Only got: He hasn't got any better.", American "Usually gotten for the meaning 'become/obtain', got for 'possess': He hasn't gotten any better. I've got two brothers."
Prepositions of time: British "at the weekend, on a course, at university", American "on the weekend, in a course, in college"
Comparisons: British "different from or different to", American "different from or different than"

-our → -or: colour / color, favourite / favorite, neighbour / neighbor
-re → -er: centre / center, theatre / theater, metre / meter
-ise → -ize: organise / organize, realise / realize, recognise / recognize
-ogue → -og: catalogue / catalog, dialogue / dialog, analogue / analog
Doubled consonant before -ed/-ing/-er: travelled / traveled, cancelled / canceled, modelling / modeling
-ence → -ense (as a noun): defence / defense, licence / license, offence / offense