(b) persons entitled to a Category B old-age pension under UK law are also entitled to the calculation of a Class A pension entitlement, in accordance with a provision of the agreements providing for the determination of this right: migrants sent to the United Kingdom from a country with which the United Kingdom has a mutual social security agreement (sometimes called a double intervention agreement or totalisation agreement). , NIC may not be obliged to pay in accordance with the terms of the specific agreement. The countries with which the United Kingdom has such agreements are listed above. The most notable exception to the territorial rule is called a detached work rule. Under this rule, a worker whose employer requires his temporary relocation from one country to another to work for the same company continues to pay social security contributions and retains insurance coverage exclusively in the country from which he has moved.1 According to almost all totalization agreements, the duration of such a transfer cannot be expected at the time of the transfer. to exceed 5 years. This rule ensures that workers who work only temporarily in the other country continue to work in their home country, which remains the country of their greatest economic link.2 On the other hand, workers who change countries permanently are insured under the country of destination regime. By mutual agreement, the two countries can agree to extend the five-year period for temporary missions abroad on a case-by-case basis, but extensions beyond two more years are rare. In 1977, labour-level immigration patterns were very different from those of 2018, and most trade and multinational relations in the United States then focused on Western Europe.
Therefore, Section 233 was adapted to the social security systems of Western Europe at the time. The first two agreements, in which the United States entered with Italy and West Germany, preceded the adoption of Section 233. That is why this scheme was designed with the social security systems of these two countries in mind. Both countries had traditional Bismarck contingency systems that covered almost all of their workforce.