"At the clinic you will be offered pre-test counselling, which is the chance to talk with someone before the test. You can talk about what you think your result might be, what risks you think you have taken and how you�d react to either a positive or negative result.
Then if you still want the test, a small sample of blood is taken from your arm.
Getting the result
How quickly you get the result depends on the clinic. Some places, like THT Fastest clinics, can tell you the same day or the next day. Many clinics will have your result within a week.
Whatever your result it will not be usually given over the phone or by letter: you will need to go back to the clinic.
The next steps
After hearing your result you should be given post-test counselling, which is the chance to talk to someone about how you feel about your test result. Your result is confidential: no-one else will be told without your permission, including your partner if you have one, your doctor or the immigration authorities.
If your result is positive you will be given support and help with finding out what to do next, including seeing a doctor to talk about whether taking anti-HIV drugs is a good idea"
http://www.tht.org.uk/informationresources/hiv andaids/testingforhiv/whattoexpect/