Your numbers are way off. It's:

    Basic rate of 20% on earnings between £12,571 and £50,270.
    Higher Rate of 40% on earnings between £50,271 and £125,139.
    Additional Rate of 45% on earnings from £125,140. (this is from the tax year starting next week, it used to be £150k instead of £125k)

You also gradually lose your tax-free allowance if you make over £100k so there's a weird dead zone in which your marginal rate is something like 60%.

Then there's NI which is effectively tax too but isn't listed in the bands above. Someone on £150k is paying 40% tax and NI (total, not marginal). Not quite half but it's not low either.

(You could get to more than 50% deductions if you factor in student loans)