I posted about this problem a few months ago, where the water level in the cistern was filling up above where it should stop, and then overflowing into the toilet. At that time it seemed to have sorted itself out and went back to normal.
Now this time it has been overflowing for about 4 days and has not shown any signs of stopping.
I followed the destructions from this manual:
It is the second problem down the list on the left hand side. I have adjusted the vertical bar up as far as it will go so the the float goes high up, and then down so the the float hardly moves or lifts.
The water level is still overflowing and now I am at a loss as to what to do next.