The Double Taxation Treaty between Bulgaria and the UK

Just to reiterate: it is possible to be tax resident in more than one country at the same time. In this case you could end up liable to pay the same tax in both countries. Also, a particular item of income could, under each country’s different rules, be taxable in both the country in which it is sourced and also in the country in which the recipient of that income is resident.

For these reasons, many countries have concluded agreements called double taxation agreements with other countries to protect individuals from being required to pay tax twice. Bulgaria and the UK have such an agreement.