A damning report into the levels of stigma being faced by people with HIV in Britain has led to calls for the government to produce a strategy to tackle discrimination.

Researchers found that one in five people with an HIV diagnosis had been harassed, threatened or verbally assaulted in the past 12 months. Many reported ignorance and prejudice from within the medical profession, particularly from GPs and dentists. One in five reported being denied medical treatment because they had HIV.

In findings to be unveiled in parliament tomorrow, The People Living With HIV Stigma Index, a two-year research project funded by the Department for International Development and the International Planned Parenthood Federation, found that only 39% of people felt confident that their medical records were being kept confidential, with 18% saying their HIV status had been revealed without their consent.

Lisa Power, head of policy at the Terrence Higgins Trust, said that the public was more ignorant about HIV than a decade ago. "This research is really important because it's about people's perception of the prejudice they face.

"We did have a good education programme in this country, but that's all gone to pot. The UK has slipped from being a shining beacon of HIV prevention programming and education, to being behind everyone else in Europe. While the General Dental Council gives its members quite clear advice on HIV, we still have dentists refusing to see patients or, which is quite common, asking them to wait until the end of the day for an appointment, apparently so the instruments can be sterilised twice.

"With far more contagious things around, like hepatitis C, it's an insult to anyone using a dentist's surgery if everything is not completely sterilised between each patient. People with HIV can lead long lives, have healthy children, but still they suffer higher levels of unemployment and relationship breakdown, more poverty, more depression and a lot of that is down to stigma, not to the actual virus."

Figures released on Friday by the Health Protection Agency showed the numbers of people living with HIV in the UK had reached an all-time high of 83,000, an 8% rise on the previous year. Of that number, 27% will not know they have the virus because the figure was reached by scientists anonymously testing random blood samples.

It is a long way from the forecasts made in 1984 of millions of people infected and dying, at a time when Britain had only 108 cases of Aids and 46 deaths. The country was gripped by fear, leading to incidents that included the fire brigade union telling members to stop mouth-to-mouth resuscitations of gay men, to patients facing isolation wards.

Even today, one London participant in the Stigma Index research said: "When the nurse put on two sets of gloves I was so humiliated – who taught her to do that?"

Another woman, who lives in a small town in Wales, told the Observer that she used health services miles away from home to protect her child from gossip at school.

"It would be round the town in a flash and yes, living with secrecy can be tough, but I think the stigma and ignorance would be far worse. Once you tell people, you can't take it back and it's too big a risk for me."

Alastair Hudson, 41, a researcher on the project, was taken aback by the stories. "People feel battered by their experiences. It was a diversity of people, from all sorts of ages and backgrounds, up and down the country, but a lot of the stories were similar, people they were coming into contact with didn't understand even the basics of HIV.

"The advertising campaigns of the 80s had a profound effect and people were scared, but the epidemic has changed so much and people's knowledge hasn't. One guy said, 'HIV is a diagnosis, not a lifestyle choice'. We don't want to normalise the virus, but we do want to make sure it's not forgotten."

However, the findings were not all negative. More than 60% of respondents said they felt they could change attitudes if they challenged discrimination. "The vast majority of people living with HIV, 84%, are also working to support each other. It was interesting that although 80-odd% of people knew where to go to access HIV support, only 23% did, which I think means people are empowered enough to look for their own support. There's far less of this victim thing than there was," said Hudson.

On the basis of the research, the all-party parliamentary group on HIV and Aids is calling for a cross-departmental government strategy to tackle discrimination. Its chair, David Borrow MP, said: "Stigma is rife in Britain and the NHS has an opportunity to lead the way in tackling it. Discrimination on the grounds of a health condition is totally unacceptable anywhere, but the public sector has a special responsibility to treat everyone it serves with respect."

Andy Burnham, the health secretary, welcomed the report, which he will launch in the Commons tomorrow.

"Effective treatments have transformed the lives of people with HIV and many more people with HIV can plan for their future with more certainty. But even in the UK, individuals and families affected by HIV can experience stigma and discrimination."

Gay men are still most likely to acquire HIV in the UK, but heterosexual infections are rising, with 58% of new diagnoses in 2008 being among heterosexuals, two-thirds of whom were black Africans. The majority of infections were probably acquired abroad, with 27% having caught the virus in the UK.