I have found out recently that the reason why many of the delicious foods in America aren't being sold in the UK, or if they are being altered. It is because of the EU's laws on artificial colouring and flavours etc. So will the UK be free to import goods from America where it could not before? Or are the food laws I mentioned also part of UK legislation not just EU's.
Short answer: All EU and EU-deriver law will stay in effect, at least for some time. However, it is expected to be changes gradually.
Long answer: The status of EU law in the UK after "exit day" (currently Mar 29, 2019, but can be changed by mutual agreement) is governed by the "European Union (Withdrawal) Act 2018". This act states (among others): - EU-derived domestic legislation, as it has effect in domestic law immediately before exit day, continues to have effect in domestic law on and after exit day. - Direct EU legislation, so far as operative immediately before exit day, forms part of domestic law on and after exit day.
This is because the body of EU law is extremely large and it is impossible to have it all revised before the exit day. Also, the EU law is so entangled with domestic legal order, that it cannot simply cease to exist (there will be many, many sensitive areas without any regulation). This is expected to change gradually - by the work of the parliament ant the government (the Withdrawal Act empowers the government to change rules in some areas even without the need to pass a law in the Parliament).
But it is expected to take years, simply because of limited capacity of the government and parliament to review so many laws.