It's perfectly easy to measure the size of the prostate with either an external ultrasound or a rectal one. It sounds as though a referral to a urologist might be a good idea if your GP is shooting ducks in the dark and simply prescribing Free Flow as a panacea to shrink a prostate that only a DRE has determined might be slightly enlarged. A two week trial sounds reasonable enough but why not encourage a referral now to give yourself the option of a shorter waiting time if the Tamsulosin does not work. It sounds though rather as if the symptom is being treated.