Agreed, it varies between unis.
With both my MScs, I needed to receive an overall average of 70% plus at least a 70% average for the dissertation for a distinction.
My first MSc awarded merits, whereas my second MSc (at UCL) only awarded a pass or distinction.
Depends on the university, check with module leaders. I averaged around 65% for both MScs, but received a merit in one and a pass in the other.