Answer:
The grammatical name for the sentence "which has been in force since 1975" is:
> Present Perfect continuous tense.
> We are talking about a grammatical form also known as "present perfect progressive.
> This grammatical form presents an activity that was started in the past but continues to be performed in the present.
> The way to use the Present Perfect continuous tense is this:
-Article + noun + has been or have been + present participle and the gerund., ing.
> That is the case of the sentence of this question. Something that has started in 1975 and is ist being enforced today.
We can conclude that the Present Perfect continuous tense indicates an action that started in the past and is still active in the present moment.