The way the tax code is structured allows you to decide how much to pay and to whom.
For example, I could earn X and hit 30% tax, but I could then offset that by deciding to pay to gay rights.
If I donate Y to gay rights my effective rate of tax reduces to 25% as I have consciously decided to pay tax here.
I can also structure my income to pay myself as an employee, or as a dividend distribution.
For example.
Say I earn 100K (bad year and all that)
I can pay tax at 30% and keep 70K.
Or I can pay myself 50K into a retirement account leaving 50K balance.
I can then pay myself a dividend distribution of 25K which avoids National Insurance (Medicare/Medicaid) but still pays income tax.
I then can pay myself the remaining 25K as regular salary. I can then pay 5K to the 2nd Amendment supporting gun toting charity of choice, and am being taxed on 45K
So now I'm at 13.5% effective tax (lower actually as tax is tiered, so its more like 11-12%)
However, once I have pulled the rate down, I can consciously decide to pull it back up again by supporting certain things that I believe are important. Such as schemes to keep free milk out of the hands of bairns.
I could pay 50K into a retirement account and 40K to charity and get a tax refund.
That's accessible to you lads in blighty too, and poor people can do it too.