As a rule, a posted worker remains part of their home country’s social security system. To certify this, the employer must complete an A1 certificate and send it to the competent social security authority of that country. The A1 certificate certifies which legislation applies to the employment contract in accordance with European regulations on the coordination of social security systems. For workers outside the EU and EFTA, including the UK, different rules apply and it is advisable to consult the relevant authorities or legal experts to ensure compliance with local regulations.