Your teacher is misinformed (sorry).
Anything you can do with a Biochemistry degree, i.e. research, industry, management, journalism or whatever your careers department have told you about Biochemistry, you can do with an MPharm, but not vice versa.
You are actually narrowing down your options by doing Biochemistry as you cant also become a practicing pharmacist on top of the careers I mentioned above. You'll need higher grades for pharmacy than for biochem though and work experience in a pharmacy is an advantage.
I had to make a decision between these subjects many years ago and in the end opted for pharmacy. I always wanted a career in academic research and that's what I got, only I dont have as much debt as the biochem graduates as I locumed my way through my PhD. Unless you have an aversion to certain aspects of the pharmacy course, e.g. you hate chemistry and formulation sciences and ONLY want to do biological subjects, or you really cant bear the thought of 5 years being a student, I'd always pick a professional course like pharmacy in the current economic climate. Hope this helps.