What happens after the transition period?
Article 71 of the Withdrawal Agreement specifically provides that after the end of the transition period, personal data from individuals in the UK or the EU will be processed in accordance with the GDPR until an adequacy decision is reached by the EU.
Ideally, the UK government and the EU will negotiate a data protection arrangement that suits both parties. This could be in the form of an adequacy decision, meaning that the personal data protection regime of the UK provides appropriate safeguards. UK business operations would then enjoy uninterrupted flow of personal data with the EU and the EEA without necessitating any further safeguards.
If no such decision is reached, the UK will become a so-called third country. To this effect, EU law will require additional measures to be put in place by UK companies (e.g. Standard Contractual Clauses) when personal data is transferred from the EU/EEA to the UK in order to render them lawful.