How do I tell my recent sexual partners that I've been diagnosed with HIV?
For some people, the best way to tell their recent sexual partners that they have tested positive for HIV is by doing so face-to-face or over the phone. Many people would want to tell their sexual partners but would like to do so anonymously. Speak to your GUM clinic about contacting partners. 

Which sexual partners should I inform if I've been diagnosed with HIV?
In theory, you should tell anyone you've taken a sexual risk with (such as fucking without condoms) since you became HIV-positive. Therefore, it will depend on when you contracted HIV and what risks you may have taken since.