law: Railways Act, 1989
  51. Provision for case in which ticket is issued for class
  
  or train not having accommodation for additional passengers. 
  (1) A ticket shall be deemed to have been issued subject to the
  
  condition of availability of accommodation in the class of carriage and the
  
  train for which the ticket is issued.
  (2) If no accommodation is available in the class of carriage
  
  for which a ticket is issued, and the holder thereof travels in a carriage of a
  
  lower class, he shall, no returning such ticket, be entitled to a refund of the
  
  difference between the fare paid by him and the fare payable for the class of
  
  carriage in which he travels.