What types of legislation are there?

Initiated by backbench MPs.
Early in each parliamentary session, 20 names of MPs who wish to introduce a bill
are drawn in a ballot. Only a small number of private members’ bills become law.
Two landmark laws to originate as private members’ bills were the Murder (Abolition
of Death Penalty) Act (1965) and the Abortion Act (1967).
They have little chance of success without government backing as exec control legislative timetable and can use ‘guillotine motions’ to limit debate on certain bills, as Cameron did in 2011 on AV System.

Secondary legislation is law created by ministers (or other bodies) under powers given to them by an Act of Parliament.
It is used to fill in the details of Acts (primary legislation).
Governments often use secondary legislation to ban new substances in response to new information about their dangers by adding them to a list under the Misuse of Drugs Act 1971.