Flatmates boyfriend does serious drugs. What action can I take anonymously?

Don't do anything. Move on and let it be.

Sounds to me that you're trying to get at his woman.

Don't be jealous that he's hittin your roommate

If I were you I would report it to the police and do not do it anonymously. While I normally like annomous tips, in your case it would hurt you.

For starters, they need to know how you know about the drug use. Going to be pretty easy to figure out if you say my roommate is doing this. Second, if its annomous they might arrest you as well not knowing your not involved. Go talk to your police dept. they can try and keep your name out of the report.

How about laying down some common rules like "No drugs in the apartment"? You don't have to get the guy arrested.

i would talk Your your flat mate and tell her that you are not comfortable with drugs in the flat.

i can not see there being anything else you can do, even if you tell the Police, will they be interested in one one guy with a bit of coke

What an asshole, offering you expensive drugs for free

Tell the cops but tell them you want to remain anonymous to the Suspect

Consider moving. I think that's the best option.