I think Chemistboy and Helen have answered the question in two different ways because the question was ambiguous. Are you getting yourself confused between a PGCE, MSc and PGCert.
A PGCE is a postgraduate teacher training course, it is not a graduate degree but a vocational graduate certificate (a bit like a conversion course for those wishing to become teachers).
The MSc isn't a teaching training course, but an academic, graduate degree. So, for example, you can study an MSc in Specific Learning Difficulties, giving you specialist knowledge in dyslexia intervention etc, but without an additional teacher training qualification you won't be able to teach in a State school (i.e. most schools).
Both courses take around 1 year to complete. The PGCE may give you M-level (masters-level) credits, so you can "top up" and work towards a masters degree at a later date, as a stand alone qualification (it's a bit ambiguous how this works sometimes though....).
A PGCert. is basically part of a masters. You get PGCert, PGDip, and MSc. As Chemistboy stated, the difference between an MSc and PGDip is a dissertation (or some form of project). If you don't submit a dissertation then you will not get the MSc, only the PGDiploma. The PGCert, however, is more like part of a PGDip.
So, if we take the MSc as being the "full course", then the MSc is better than a PGDip which is better than a PGCert. Each university is slightly different, but you may find that completition of 2 modules = PGCert, completion of 4 modules = PGDip, completion of 4 modules + dissertation = MSc.
The PGCE isn't part of an MSc so can't be ranked to easily.
Does this make sense?