OMG, How do we tax the rich, its so difficult

Luisa has been thinking about the Tax Cap on charitable giving, carefully constructed to ensure very, very, very rich folk don't use charitable giving to avoid paying tax. It should probably be renamed the Dunce's Tax Cap as it is a strangely poor and superficial attempt to be seen to be trying to extract some tax from the VVVRF.  If HMG really wanted to ensure the VVVRF paid some tax at least, the simple thing to do surely is to enact a law or tax rule which says that if you earn say over £5million gross a year, no matter what your outgoings are you must pay a fixed % on that say 2% or a fixed sum, say £100k. That will force the VVVRF to pay their taxes but not interfere, [I hope] with charitable giving. I remember many years ago paying £7k in taxes in one year where I had earnt £47k - perhaps you'll say I needed a better accountant. I then discovered that someone I knew of had earnt £3.5 million in that same year and had paid £5k in tax. They obviously had better accountants, who themselves were probably tax deductible, but for me there was something very wrong with that situation. The Dunce's Tax Cap isn't going to resolve it.