From ACT Wiki
1. Delegated powers.
Law made by ministers under delegated powers given to them by Parliamentary Acts.
Sometimes referred to as secondary legislation or subordinate legislation.
2. Tax - HMRC.
A secondary source of UK tax law that is not written by parliament but usually by His Majesty's Revenue & Customs (HMRC),
3. Primary legislation.
Law created by any other subordinate law-making body, within the authority of an Enabling Act - or other primary legislation - enacted by the primary law-making body.