Besides, proportional tax (or you could call it flat tax) still puts a higher burden of taxation on the richest. (totalpolitics.com)
Equally it is not trivial to calculate exactly where the ultimate burden of taxation falls. (politics.stackexchange.com)
In 2007, the party abandoned its longstanding pledge to introduce a new 50p tax rate on the highest earners, and the following year called for a reduction in the overall burden of taxation. (theconversation.com)