These Regulations are made in exercise of the powers in section 8 of, and paragraph 21 of Schedule 7 to, the European Union (Withdrawal) Act 2018 (c.16) in order to address failures in retained direct EU law to operate effectively and other deficiencies (in particular under paragraphs (a), (d) and (g) of section 8(2) of that Act) arising from the withdrawal of the United Kingdom from the European Union.
Link: The Air Quality (Miscellaneous Amendment and Revocation of Retained Direct EU Legislation) (EU Exit) Regulations 2018
Source: Legislation .gov.uk
