Less frequent one is mixt rather than mixed, which is a great word for Scrabble (TM).
Ahhh what a great word! Mixt needs a revival! I mean, if us Brits have have burnt and dreamt, why not be consistent and have mixt too? That's the thing with British English. The language and what words people use is very inconsistent - but all British people somehow instinctively use the same inconsistencies. It's just an instinctual habit that everyone would say spelt and learnt etc... I can't for the life of me remember what we were taught in school but that must have been it!
1. Some people will only say learned, burned, spelled etc..
2. Some people will only say leant, burnt, spelt etc... (I would say this is 90%+ of Brits)
3. Some people will say learnt for the past tense and learned for the verb. e.g. I learnt Spanish at school vs I have learned to speak Spanish. I wonder if this is the correct option by the correct book of grammar? The distinction is so subtle, I'm not sure I would ever recognise it! That is, if it's even correct. Who knows?
*Actually 'learnt' is a bit of an odd one. Most Brits will say learnt for anything but the word learnED to mean something different e.g he was a very learnED man.