Just looking on the Sram site it looks like to get the 32 you need the Mid sized sram Apex or the Mid sized Rival rear mech. comparing photo's I think I have the smaller Rival that can only go up to 28. (Things are becoming clearer slowly)
The question now is do I get a new Rival rear mech or an Apex both mid size cage that can handle the 32T? My gut tells me the Apex as wiggle has it for about £45 when the Rival is about £75?