These are made by government ministers who are specifically members of the cabinet. 15 departments.
each cabinet minister has there own 'portfolio' (topic) responsible for a key area. Finance, Education, health.....
the law they make is called a regulation and approx 3000 made a year
they can cover small matters or complex and very detailed ones
SI can amend pre-existing acts of parliament
EG. the dangerous dog act 1991 --> allows home secretary to add more dangerous breeds if needed