A small group of verbs have two past tense forms – an irregular one ending in -t and used more in British English and a regular one ending in -ed and used more in American English. The most common six are burn~burnt/burned, dream~dreamt/dreamed, lean~leant/leaned, learn~learnt/learned, smell~smelt/smelled and spill~spilt/spilled. Note that the pronunciation of the vowel changes with two of these: dream~/drɛmt/ / /dri:md/ and lean~/lɛnt/ / /li:nd/. [For some reason, I missed leap~leaped/leapt.]
In general, my Australian English usage is closer to British than America, but I have consciously decided to write -ed and say /dri:md/ and /li:nd/, probably because students are more likely to understand them.
A few days ago, I was talking to an English-as-a-second-language speaker. He asked me something which required me to use the past simple of lean. Without thinking about it, I found myself saying /lɛnt/. If he is not familiar with that pronunciation, I hope the context made it clear. I said something like “I lent over to pick up a sock and when I stood up, I knocked my head on the door handle”.