As per Wikipedia “Great Repeal Bill
may refer to two items of United Kingdom legislation: Great Repeal Bill (2008 proposal), Conservative proposal which fed into the Protection of Freedoms Act 2012. European Union (Withdrawal) Act 2018, first proposed under the title “Great Repeal Bill” in 2016 by the May ministry as part of Brexit.”
This would repeal the European Communities Act 1972 and restate in The UK law of all enactments by ensuring that all law remains in force, until specifically repealed.
As a result, the same laws, regulations would apply, right after or before departure from the European Union.