When the Brexit transition period ends, the data protection laws of the EU will no longer be valid. This will lead to much weaker data protection for all Brits.
As the UK leaves the EU, regulations on how their data will be handled by the big IT giants are also affected. According to Reuters, one severe consequence will be that British users’ accounts on Google will no longer be subject to Irish law. Instead, US law will apply.
The reason Google is planning to move over the UK users is, according to the sources, that it is unclear whether the UK should comply with the GDPR or whether they should introduce new rules that could affect how user data is handled.
The US has very weak data protection and the move, therefore, means that data protection for British users would be weakened.
However, the Cloud Act, a United States federal law enacted in 2018, is expected to make it easier for UK authorities to request user data from US companies.
Google is first out, but according to people with insight into the matter, similar discussions are underway on how to handle UK user data after Brexit at other US IT companies as well.