I know that this question is closed, but just want to leave extra information for those who are looking for the same answer. On the “Direcção Geral dos Impostos” site, there are documents in English that point as a translation “Directorate General for Taxation”. I believe that if we are referring to the Portuguese institution itself is a little strange to place “HM”, since we don’t have a queen. I suggest that it can be placed something like “Directorate General for Taxation, corresponding to the “HR Revenue and Customs”. Just check
http://info.portaldasfinancas.gov.pt/NR/rdonlyres/F2D76036-A... in the “Structure and functions” section. This is just an opinion and I hope I could be of some help.