What grades do I have? In a two months I will have a bachelors degree from a German University with an degree average (Notendurchschnitt) of 1.8 or 1.9 . My programme uses ECTS Credit Points.
I am in the process of applying to British MSc programmes. They mostly require a Honours degree of "2:1" which, according to one university, is equivalent to "GPA 3.0". 

Do I pass these requirements? And is it legit for me to say in my application that I have a GPA of 1.9?

I tried to get my head around these degree specifications but was unable to.
Depends what university you will apply for. However, because the Msc is expensive in the UK, even for the British students, the students tend to look for jobs after Bsc; and therefore some universities accept students with lower grades.

Little bit of advice: Look for the courses in details to cover your interests; For example an Msc in Computer Science at one university might involve more than theory; than the same Msc at another university.