If he wasn't an employee in Germany, and as long as he is not yet of pension age, he would be a voluntary member of German public health insurance. This means that he has to pay: 14% + Zusatzbeitrag of his Krankenkasse (around 1%) for public health insurance 2.55% (2.8% if he had no child) for public nursing insurance on his entire worldwide income, i.e. also on his UK military pension, capital income, rental income, and so on. All income types on which he has to pay the above contributions are listed in here: https://www.gkv-spitzenverband.de/media/dokumente/krankenversicherung_1/grundprinzipien_1/finanzierung/beitragsbemessung/2017-11-07_FK_Beitraege_NDS_Einnahmekatalog_240SGBV.pdf   *************************************************************   Since he is an employee in Germany, he has the advantage that he is a mandatory member of German public health insurance, which means that he only has to pay: 7.3% + Zusatzbeitrag of his Krankenkasse and 2.8% (2.55% if you had a child) for public nursing insurance on German gross salary, 14.6% + Zusatzbeitrag of his Krankenkasse and 2.8% (2.55% if you had a child) for public nursing insurance on German company pension (if he has one), 14.6% + Zusatzbeitrag of his Krankenkasse and 2.8% (2.55% if you had a child) for public nursing insurance on UK company pension (if he has one),  14.6% + Zusatzbeitrag of his Krankenkasse and 2.8% (2.55% if you had a child) for public nursing insurance on UK military pension (I assume that they will treat it like a German Beamtenpension, and the rare German Beamter who opted for public health insurance has to pay the "allgemeinen Beitragssatz" of 14.6% on it, see half-way down this page: "Denn bereits seit dem Jahr 1983 müssen Rentner ebenfalls einen Beitrag zur gesetzlichen Krankenversicherung bezahlen. Dieser orientiert sich, wie zu Erwerbszeiten auch, an der Höhe des monatlichen Einkommens des Pensionärs. Seit dem Jahr 1997 gilt sogar der allgemeine Beitragssatz.") He will not have to pay German public health&nursing contributions on his other worldwide income like, for example, capital income and rental income.     As soon as he reaches normal pension age, he will not be a special case like TP, since he will also draw a German public pension, having worked as an employee in Germany for more than 5 years. So no hope of free German public health insurance for him.   Since he will have spent at least 90% of the second half of his working life in an EU public health insurance (NHS and now the Krankenkasse), as soon as he reaches pension age he will become a member of the KVdR (Krankenenversicherung der Rentner), i.e. a mandatory member of German public health, and will have to pay: 7.3% + Zusatzbeitrag of his Krankenkasse and 2.8% (2.55% if you had a child) for public nursing insurance on German public pension, 7.3% + Zusatzbeitrag of his Krankenkasse and 2.8% (2.55% if you had a child) for public nursing insurance on UK public pension, 14.6% + Zusatzbeitrag of his Krankenkasse and 2.8% (2.55% if you had a child) for public nursing insurance on German company pension, 14.6% + Zusatzbeitrag of his Krankenkasse and 2.8% (2.55% if you had a child) for public nursing insurance on UK company pension,  14.6% + Zusatzbeitrag of his Krankenkasse and 2.8% (2.55% if you had a child) for public nursing insurance on UK military pension (I assume that they will treat it like a German Beamtenpension, and the rare German Beamter who opted for public health insurance has to pay the "allgemeinen Beitragssatz" of 14.6% on it, see half-way down this page: "Denn bereits seit dem Jahr 1983 müssen Rentner ebenfalls einen Beitrag zur gesetzlichen Krankenversicherung bezahlen. Dieser orientiert sich, wie zu Erwerbszeiten auch, an der Höhe des monatlichen Einkommens des Pensionärs. Seit dem Jahr 1997 gilt sogar der allgemeine Beitragssatz.")   For details please read: