At the moment UK follows many (not all) EU rules because the UK Parliament has put them into UK law. In most cases UK voted in favour of these regulations, and helped influence, develop and specify them. Obviously we have now thrown those rights away.
UK can, if it wishes, standardise on 3-pin connectors for phone chargers, on chlorinated chicken, and on hormone-grown beef. Nobody will prevent it, and the EU will not order it to stop.
Obviously it will have great difficulty if it wishes to export them to EU. So it will probably continue to follow the EU, in its own interests.