The House of Commons Library has produced a very succinct, useful summary of the current position of the interface between UK & EU employment law and the Government's position on the matter.

The author notes that

"the main point to note is that EU-derived employment rights featuring in primary legislation would be relatively insulated from the effects of leaving the EU, although would be newly susceptible to the possibility of change. Greater uncertainty surrounds the implications of Brexit for secondary legislation, in which much employment law is contained."

On that theme, the report also highlights the "somewhat thornier – and important - question" concerning the status of European Court of Justice (ECJ) case law, pointing out that

"Post-Brexit, UK courts would no longer be required to follow existing and future ECJ decisions, and may merely regard them as having persuasive force. A potential consequence of that approach may be the re-litigation of controversial judgments, such as those relating to the calculation of holiday pay. "

You can read the full briefing paper here.