Don't know if this helps, but my PGCert was 60 credits (1 yr p/t), my PGDip was 120 credits (1 yr f/t) and I think a Masters is roughly 160-180 depending on how many modules/credits awarded (1-2 yrs?) The PGCert n PGDip were for conversion to psychology from an arts degree, I had to have the former before I was admitted onto the PGDip course.
You'd be best off talking to someone at the Uni. I'd think the exiting with either the PGCert or PGDip would depend on how much work you had completed up to a certain point.
Good luck!