Hi there, 

I've been on roaccutane for almost 6 months now on NHS as well. It took me a long time to actually get referred to the dermatologist because I only had mild but persistent acne. I was on many antibiotics and creams prescribed by my GP for about 3 years before being refereed to the hospital. I've had a very good experience with the dermatologist I've been seeing and the process is straightforward

1. Blood test and urine test (if you are a female) on your first appointment, initial discussion about the state of your skin, questions about your height and weight, long discussion about side effects etc, you get your prescription to pick up the medicine 
2. Monthly blood tests which I've been doing a week before my appointments with the doctor, no food, no coffee  before the blood tests 
3. Urine tests (if you are a female) which are done on the day of your appointments
4. Monthly appointments with the dermatologist to discuss your blood test results, preagnancy test results, side effects and evaluate the state of your skin as well a your mental state (depression, mood swings etc) which I've never experienced anyway 
5. You get your prescription after each appointment

I had my appointments every 28 days. I'm due to finish my course in 3 weeks and my last check up is in December. 

Let me know if you have any questions. 
Good luck! Roaccuatne has changed my life. I was so scared at the beginning but I should have done it earlier! Be prepared for some annoying side effects but for me it was all worth it. I did not experience the IB at all which I was panicking and worrying about like a crazy person. 

Good luck!