any experts on tax questions regarding immigration

I am confused on three questions if anyone can shed some light
1. What is High tax
2. contrubution tax, 300000 profit is 20 percent what is it between 300000 and 1500000 and how is it calculated
3. How do you calculate National Insurance which is paid be the employer (what percentage on the salary and commission incentive)
Did check hmrc web site but got more confused than before
Regards

1) Study "Tax Bracket"
2) Refer this from a Professional Accountant
3) Study this : http://www.which.co.uk/money/tax/guides ... i-you-pay/

Thank you