Pharmacy (MPharm) is a masters degree, and if you do the sandwich course (this includes a year of professional pre-registration training) it is 5 years. Then after that you have to sit a board licensing exam which is set by the professional regulator (GPhC) before you can join the register of pharmacists.
You would have to start at the beginning, maybe there are some universities that allow you to start from MPharm2 (second year), if this was the case then it would take you four years minimum (assuming you pass everything first time including the licensing pre-reg exam) to become a pharmacist.
Most, if not nearly all universities would require you to start from the very beginning in which case it is 5 years to become a pharmacist.