Once Brexit becomes official, and should it be a “hard” Brexit, all British citizens will be considered foreigners in the European Union. As such, all British citizens, who wish to have either a residency or a second citizenship in a European country, will have to apply for it like any other foreigner from a country outside the EU. In your specific case, having a Portuguese residency through the golden visa program would be the best option, as it only requires you to stay in Portugal for seven days per year, unlike the general residency programs, which require a mandatory stay of six months. Also, a residency issued under this kind of program allows you to freely work in Portugal. Should the withdrawal agreement be accepted between the UK and the EU, as it is, it will integrate protective measures for the so-called “cross-border workers”.
