Because I like doing things the English way

• acknowledgement rather than acknowledgment
• either ageing or aging is fine (but aging sounds like ah-ging, which is gross)
• aeroplane, not airplane, never airplane
• aluminium rather not aluminum
• anaemia rather than anemia
• artefact rather than artifact
• blonde rather than blond
• burnt and burned are both acceptable (apparently)
• cancelled, travelled, labelled, counsellor, -- yeah, you get it, double 'L's!
• catalogue rather than catalog, and programme rather than program
• centre rather than center, fibre rather than fiber, metre rather than meter
• dependant = noun, dependent = adjective
• diarrhoea not diarrhea
• dietician and dietitian are both accepted
• doughnut not donut
• dreamt and dreamed are both accepted
• enquiry and inquiry are both accepted
• enrol rather than enroll and fulfil rather than fulfill
• foetus rather than fetus
• focussed, focussing
• gynaecology
• judgement, ok, but NOT arguement. argument is correct for both british and american english
• licence = noun, license = verb, same goes for practice and practise
• fulfilment rather than fulfillment
• manoeuvre rather than maneuver
• practise - verb / practice - noun / You 'S'tir (verb) your 'C'offee (noun) -- US, it's just practice all the time
• pretence rather than pretense
• pyjamas rather than pajamas
• sceptical not skeptical
• speciality not specialty
• sulphur not sulfur
• towards not toward
• tyre not tire
• yogurt, youghurt, youghurt, youghourt... really depends on how you want to spell it, in this case
• defence and offence, with 'C's instead of 'S's. defense and offense are spelt that way for easier sports-language use, e.g. 'defensible, etc.
• enquire = casual, inquire = formal