law: Code of Criminal Procedure Act, 1973
  
  427.Sentence on offender already sentenced for another offence.-
  (1) When a person already undergoing a
  
  sentence of imprisonment is sentenced on a subsequent conviction to
  
  imprisonment or imprisonment for life, such imprisonment or imprisonment for
  
  life shall commence at the expiration of the imprisonment to which he has been
  
  previously sentenced, unless the Court directs that the subsequent sentence
  
  shall run concurrently with such previous sentence:
  
  Provided that where a person who has been sentenced to imprisonment by
  
  an order under section 122 in default of furnishing security is, whilst
  
  undergoing such sentence, sentenced to imprisonment for an offence committed
  
  prior to the making of such order, the latter sentence shall commence
  
  immediately.
  (2) When a person already undergoing a sentence of imprisonment for life is
  
  sentenced on a subsequent conviction to imprisonment for a term or imprisonment
  
  for life, the subsequent sentence shall run concurrently with such previous
  
  sentence.