My 56plate GTi says to use 95RON on the fuel cap.
From what I have read Tesco fuel is supplied by Greenergy of which Tesco own 25%, the fuel is 5% bio-ethanol and it is believed Sainsbury's fuel is supplied by BP.
I got my GTi last month and have been runningit on 95 RON for the last few refills, intend to experiment with some different fuels an see if I notice a difference.