footage has been released of the moment barry lyttle punched his brother .
altercation left barry 's younger brother patrick lyttle fighting for his life .
video shows patrick pushing barry and the latter retaliates with one punch .
patrick 's head snaps back before he falls and hits head against pavement .
it also shows a distressed barry cradling brother while trying to revive him .
prosecutor called for barry to get jail time as patrick pleaded to spare him .
barry lyttle , 33 , has pleaded guilty to causing grievous bodily harm .
incident between the two brothers happened on january 3 in king 's cross .