4. Application of Regulations

(1) Subject to paragraph (2), these Regulations apply to a complaint submitted on or after the coming into operation of these Regulations relating to a question in dispute involving income or capital earned in a tax year commencing on or after 1 January 2018.

(2) These Regulations may, where the Commissioners so agree with the competent authorities of relevant Member States, apply -

(a) to a complaint submitted before the coming into operation of these Regulations, or

(b) to a complaint involving income or capital earned in a tax year commencing before 1 January 2018.