I should add that option (b) is the approach we have largely taken to leaving so far. The European Union (Withdrawal) Act 2018 brought a significant amount of EU law into UK law, so we have adopted it and once we leave we will continue follow it, but are free to change it at a later date. It is also what Teresa May is offering Labour - incorporate the current workers' rights etc into UK law, and as new EU laws are proposed the UK Parliament would consider whether to adopt them.