ECSH44175 | The register: premises which do not need to be registered
From HM Revenue & Customs · Economic Crime Supervision Handbook
A business does not need to register any premises that are outside the UK or if the premises are only used for:
Storing business records.
Training employees.
Generally managing employees.
However, if any part of processing transactions takes place in that location, such as paperwork being completed, the business will need to register that address as premises.