Main Points of the Brexit Deal and Social Security for Cross-Border Workers

For situations existing on or before 31 December 2020, the old rules will continue to apply, provided there is an uninterrupted link between the EU and the UK.
For new cases (i.e. from 1 January 2021) the so-called Protocol on Social Security Coordination applies.
The main starting point is and remains that a person can only be insured in one state at a time and also only pays his compulsory contributions in one state.
This Protocol regulates the social security position of EU and UK nationals in almost the same way as before 1 January 2021 (via EU Regulation 883/2004).
The basic rule is that the state of employment applies, except for civil servants and persons who do not perform any duties.
The same rules apply to secondment as in Reg. 883/2004, unless states wish to deviate from this.
When working in multiple states, the rules are almost identical to those in Reg. 883/2004.
Rules may be different for (workers in and from) Norway, Switzerland, Iceland and Liechtenstein