Start by deciding whether the issue affects controller/processor roles, lawful basis, transparency, DPIA, data-subject rights, breach notification, IDTA/Addendum transfers, children data, or ICO enforcement exposure. The International Data Transfer Agreement (IDTA) is the UK's standalone contract for restricted transfers, while the UK Addendum lets you use the European Commission's Standard Contractual Clauses for UK transfers. Use the IDTA for a UK transfer tool on its own, or the Addendum when you want to rely on the EU SCCs with UK-specific changes.
Keep the UK GDPR source, DPA 2018 context, role map, lawful-basis analysis, DPIA/rights/breach/transfer evidence, and ICO-facing record together.