qs, In the UK the first 35000 is 20% the next 150000 is 40% and above that is at 50%, you can claim allowance but because their earnings are so high it won't be there and they may have benefits in kind that are taxable. And you have to work out NICs
So you probably were earning after allowances within the 35000 band hence your 20% tax. Only gift aid donations could increase the bands, btw I'm a chartered acccountant.
Although there are tax avoidance schemes, and the latest budget wants to move the 50% rate to 45%