If the UK leaves the EU in March 2019 with no agreement in place regarding future arrangements for data protection, there would be no immediate change in the UK’s own data protection standards. This is because the Data Protection Act 2018 would remain in place and the EU Withdrawal Act would incorporate the GDPR into UK law to sit alongside it. Companies would continue to be able to send personal data from the UK to the EU.
However, the legal framework governing transfers of personal data from organisations (or subsidiaries) established in the EU to organisations established in the UK would change on exit. Companies would need to take action to ensure EU organisations were able to continue to send you personal data.