Under data protection laws, organisations should not transfer data outside of the EEA or the UK to a country or recipient where the GDPR does not apply, except in very limited circumstances. The restriction applies no matter who you are and no matter how much personal data is being transferred or type of personal data being transferred.
After the Brexit transition period, when the UK officially leaves the EU, the UK will become a "third country" for the purposes of the GDPR. This means that any data transfers from the EEA to the UK will also be restricted. There are some exceptions to this restriction and one of those is by using the Standard Contractual Clauses.
To facilitate ex-EEA transfers of personal data, the European Commission has approved a set of standard contractual provisions called the Standard Contractual Clauses ("SCCs") that ensure parties properly protect personal data that is transferred outside of the EEA. There are SCCs that cover controller to controller and controller to processor transfers. If there is a transfer of personal data outside of the EEA (including to the UK), you should consider whether or not the SCCs should be implemented between the parties.