Maritime certificates of competency
The UK is a third country and Finland cannot issue endorsements recognizing certificates of competency issued by the UK in accordance with the STCW Convention until the European Maritime Safety Authority (EMSA) has audited the UK and the European Commission has recognized the UK and added it to the list of recognized countries.
Nevertheless, the UK may potentially recognize and endorse Finnish certificates of competency based on the STCW Convention.
However, in the future Finland will not be able to recognize, under the Professional Qualifications Directive, national non-STCW certificates of competency issued by the UK.
For maritime qualifications, what matters is not the nationality or place of domicile of the person, but rather the state authority which has issued the qualification.