I actually think OP is very naive, to think that shenis safe from contaminated or 'cut' drugs because she is a regular. You are nothing more than a £50 note to that person.
A drug dealer does not have morals or a code of ethics. He does not value you or your life. He is selling you literal poison to your body. And he will be involved in other crimes. Most likely violent or sexual.
He is not your friend or a trusted source. He is not a pharmacist or a GP.
He is a criminal and his objective is to get as many people as he can addicted to have a regular income.
And his profit margin is more important than your safety so I can guarantee you are not getting some Tony Montana in a hot tub type coke in England from a scroat in a Gymking track suit. You are getting something that will be cut and laced with cheap fillers, that are just good enough to keep you addicted.
I know you probably thought you were really cool starting this thread. Cool and controversial.
But its honestly just sad. Take that £50 a week and do something positive before you have a reaction or incident that you cannot come back from.