law: Arbitration Act 1940
  Section 15
  Termination of Mandate and Substitution of Arbitrator
  (1) In addition to the circumstances referred
  
  to in section 13 or section 14, the mandate of an arbitrator shall terminate -
  (a)  where 
  
  he withdraws from office for any reason; or
  (b)  by 
  
  or pursuant to agreement of the parties.
  (2) Where the mandate of an arbitrator
  
  terminates, a substitute arbitrator shall be appointed according to the rules
  
  that were applicable to the appointment of the arbitrator being replaced.
  (3) Unless otherwise agreed by the parties,
  
  where an arbitrator is replaced under sub-section (2), any hearings previously
  
  held may be repeated at the discretion of the arbitral tribunal.
  (4) Unless otherwise agreed by the parties, an
  
  order or ruling of the arbitral tribunal made prior to the replacement of an
  
  arbitrator under this section shall not be invalid solely because there has
  
  been a change in the composition of the arbitral tribunal.