Each British police force went on to form its own Special Branch , the largest being that of the Metropolitan Police until it was merged with the Metropolitan Police Anti-Terrorist Branch ( SO13 ) to form Counter Terrorism Command or SO15 in 2006 .
The Metropolitan Police had their own Special Branch , until it was merged with the Metropolitan Police Anti-Terrorist Branch ( SO13 ) to form Counter Terrorism Command or SO15 in 2006 .