Chris (April 2011) -- your advice was a lifesaver - I have inserted your useful tip below because the advice was so useful. Have a whole bunch of family arriving soon for a 70th birthday and your advice here saved the day. Now two operating toilets in the house.
RE: REMOVING CISTERN LID FROM VISTA AVALON toilet (thanks to Chris advice below 2011).
if it is a dual-flush system (so there's a large button and a small button), you push the large button down, and while it's down use a flat head screw driver to pop the small button out, then do the same for the large button (using the space where the small button was to lever the big button out) and then you use the screw driver to unscrew the screw at the bottom holding the ring in place and then you can remove the cistern
RICHARD OF MELBOURNE
September 2015