Sandy is employed as an architect and received the following income during the tax year 2020/21: i) Salary - £80,000 (after his employer had deducted PAYE of £24,950). ii) His employer provides Sandy with a parking space at work. If Sandy had to pay for his own parking close to his office, the annual cost would be £600 per annum. iii) Bank interest of £900. iv) Building society interest of £400. v) Dividends from a UK company of £3,400. vi) Premium bond prize of £50. 

During the year, Sandy made a charitable donation of £600 under the Gift Aid scheme; and he paid his annual £300 subscription to the architects' professional body which is  approved by HMRC.

Required: 

a) Prepare the income tax computation for Sandy for 2020/21, showing the income tax liability and the tax due to be paid. 

b) Appraise the UK income tax system with refence to Adam Smith's canon of equity.