The sting in the tail of it is this bit:
"The bad news is that if the sale price is higher than the reference value then the tax will be based on the sale price. However, if the sale price is less than the reference value it is the latter that will count. In other words, there is no win, win on this. You will always be charged at the higher value"
Best you can hope for, if selling, is that you sell for more than this "reference value", at least that way your percentage charge won't go way up. Imagine selling for 1/2 of the reference value, because property prices have taken a dive just at the wrong time, it would effectively double your taxation hit. No way is this a fair and equitable system.