Anthony Rayworth 's reply:
Whilst I cannot comment on individual institutions, I can advise the following:
Genuine Post-Graduate education is that which follows the achievement of a BA (Hons) or a BsC (Hons) or equivalent; these are NQF Level 6 qualifications. A Post-Graduate Qualification is, therefore, a NQF Level 7. Be cautious when applying for any 'Post-Graduate Certificate' or Masters Degree that is not NQF Level 7. Visit http://en.wikipedia.org/wiki/National_Qualifications_Framework for clarification of Levels.
A PGDip is often perceived as a 'bridge' between BA (Hons) and MA. As the only difference between the two qualifications is the completion of a Masters Project or equivalent, I would recommend that you study for an MA in Interior Design. It is recognised by more employers and in more countries than a PGDip.
I hope this helps