U Wot M8 is just text
slang for ' You what mate?' - a confrontational phrase used mainly in Northern
England. Normally in response to another confrontational phrase - see example below. It does make sense though is abbreviated, it is a shortened of "YOU are going to do WHAT, MATE?" Mate being the obvious indicator that there is trouble afoot. This abbreviation is probably the cause of much confusion to the American audience since they have similar difficulty with 'half two' meaning half past two (not
one or
one thirty like some of the common guesses).