NIM33360 | Special Cases: International: Going to or Coming from Abroad: EEA Regulation 1408/71 (before 1 May 2010): self-employed in 2 or more Member States
From HM Revenue & Customs · National Insurance Manual
Note: This page is under review and the content may only be appropriate to periods beginning before 1 January 2021 and for those covered by a Withdrawal Agreement. A new International NICs manual is under development and will be published in due course.
Article 14a.2 of Council Regulation [European Community (EC)] No. 1408/71
If a person is normally self-employed in 2 or more Member States, liability is determined by either
their country of habitual residence if they carry on any part of their activity there or, if not,
the Member State in which they pursue their main activity.
Forms E101 will be issued for such workers.
For more information on applying for an E101 see GOV.UK.