Moreover this is subordinate or delegated indirect legislation.
In fact section 2 of the Interpretation and General Provisions Act specified subsidiary legislation as 'any legislative provision as together with a transfer or delegation of powers or duties made in exercise of any power in which behalf conferred by any written law through way of by-law, notice, proclamation, order and regulation, rule of court or other instrument'. The by-laws, notices, orders, regulations, rules and other 'instruments' constitute the body of the laws known like subsidiary legislation.
At mostly section 30 of the Constitution offered that 'the legislative power of the Republic as of England shall vest in the Parliament', then it is not possible for Parliament itself to enact all the laws that are mandatory to run all the affairs of this country. However many Acts of Parliament essential much detailed work to implement and manage them. Thus in such a case the Act is drafted so as to gave a broad framework that will be filled in later through subsidiary legislation made through Government Ministers or other persons under powers conferred on them through the Act.