People who are concerned that they might have HIV can legally test themselves in the comfort of their own homes from today.
Until now it was illegal in the UK to do an HIV test at home and read the result yourself - people could take a sample themselves, send it off for testing in a laboratory and receive the result at a later date.
But a change in the law, which comes into effect today, will mean people can perform a simple saliva test at home which will quickly give the user a "negative" or a "positive indication" result.
While the law changes today, no kit has yet met stringent quality standards for approval for UK use.
Sexual health charities have said that a home testing kit should be available by the end of the year or early next year.
Experts hope that making the tests more readily available will help reduce infection rates.
There are about 100,000 people infected in the UK, including around 22,000 who have the human immunodeficiency virus but are not aware they have been infected.
Deborah Jack, chief executive of the National Aids Trust, said: "I really hope the introduction of self-testing kits will increase the level of HIV testing in the UK and help reduce the worrying level of undiagnosed HIV.
"Currently one in five people in the UK who have HIV don't know they have have it and over half are diagnosed late, meaning they have had HIV for at least four years.
"Being diagnosed late means you are more likely to get ill and more likely to unwittingly pass the virus on to sexual partners.
"Thanks to excellent medication, HIV is no longer a death sentence. An HIV diagnosis doesn't mean that you have to leave your job or give up hope of having a family.
"In fact, if diagnosed early, someone with HIV can now have a normal life expectancy.
"People shouldn't put off testing because they are worried about what a positive diagnosis might mean for them. Instead they should be worrying about remaining undiagnosed - and the lasting damage it could be doing to their health."
Michael Brady, medical director at Terrence Higgins Trust, said: "We welcome this law change, which will give people another choice about how and where they test for HIV.
"The success of our HIV home sampling scheme has shown that many people who have never tested before, or who have been putting off a visit to the clinic, are willing to test at home.
"With HIV transmission in the UK largely driven by the 22,000 people who remain undiagnosed, anything that provides them with another option to test and access effective treatment is welcome.
"It is vital that HIV self-testing kits offer high-quality information, including how to obtain practical and emotional support and how to quickly access specialist HIV services.
"We will be working closely with manufacturers to ensure that any kit that comes to market meets the very best standards of patient information."
Professor Jane Anderson, Public Health England's lead for HIV, sexual and reproductive Health, said: "At the moment no HIV self-test kits have been approved for UK sale.
"However, when these become available, the option of HIV self-testing will be another step forward in tackling the HIV epidemic.
"To make sure this is done safely it is crucial that everyone whose self-test indicates they may have HIV gets their test confirmed by a healthcare professional. People who are HIV positive must have prompt access to appropriate advice, care and treatment."