For example, we will introduce a customs bill to establish a framework to implement a UK customs regime. The requirement for a UK customs regime cannot be met merely by incorporating EU law – and would benefit from the intensive parliamentary scrutiny given to primary legislation. Similarly, we will introduce an immigration bill so nothing will change for any EU citizen, whether already resident in the UK or moving from the EU, without Parliament’s approval. This is in line with our overall approach to the Great Repeal Bill – not to make major policy changes through or under the Bill, but to allow Parliament an opportunity to debate our future approach and give effect to that through separate bills. New legislation will be required to implement new policies or institutional arrangements that go beyond replicating current EU arrangements in UK law.

High

https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/604516/Great_repeal_bill_white_paper_accessible.pdf

Chapter 1, Paragraph 1.22