Just found this.
EBC Redstuff should be used at both front and rear for optimum balanced brake performance but if this is outside your budget see the "Can use" table below:
On Front OK to fit or have on rear
Original Ultimax only
Ultimax Ultimax or original
Greenstuff Greenstuff, Ultimax or Redstuff or original
Redstuff Redstuff or Original
Yellowstuff Yellowstuff,Green,Red,Ultimax or original