Government policy states that having HIV can never be used as a reason to refuse any applications for a visa, leave to remain or asylum.
If you apply for asylum, the application must be based upon a fear of persecution for reasons of race, religion, nationality, membership of a social group or political opinion.
If you are applying for leave to remain solely on human rights or compassionate grounds, the Home Office will consider several factors together, often including your HIV diagnosis. The relevance of this will depend upon the extent and severity of your health problems and symptoms. The availability of anti-HIV medicine and HIV care in your home country will also be taken into account.
A good immigration lawyer can advise you on the likelihood of you being granted leave to remain in the UK.
In either of these cases disclosing your HIV status to officials may help you get accommodation and support. In cases where someone is very ill or vulnerable this may be from the local authority of the area where you live.
Most people, however, are supported by the UK Border Agency (formerly known as the National Asylum Support Service) which disperses people to areas of the country where there is available housing stock. You cannot choose where you live and you are very unlikely to be housed in London.
The current policy of the UK Border Agency is to consult your HIV doctor to make sure there will be appropriate health care in the place you will be sent to. Therefore it is useful if any immigration officials dealing with your case or deciding where you will live are aware of your HIV status, to ensure you get the correct medical care.