if you have been exposed to the hiv virus or think you may have, then you should get checked out at your local GUM clinic, telephone number will be available from NHS direct.
At a GUM clinic you don't have to give your name and no personal details will be revealed without your sayso.
In some people exposed to the HIV virus, a 'seroconversion illness' (where the person will develop antibodies to the HIV virus, going from HIV negative to HIV positive) will follow, this is generally of non specific flu-like symptoms (feeling lousy, headache, neck swelling, fever etc).
The terence higgins trust provides more information, they have a website, try searching for it in google.