Media playback is not supported on your device.
David is one of at least 15 people who tested positive for HIV while waiting to access Prep.
At least 15 people in England tested HIV positive while waiting to get a seat on a pill that prevents the disease.
Pre-Exposure Prophylaxis (Prep) is a daily pill that can prevent a person from contracting HIV.
England is the only place in the UK where places in a trial to access the drug by the NHS are restricted.
The Department of Health said plans are underway to make the drug more widely available next year.
Prep is available for free to high-risk patients in Scotland and the British HIV Association, which represents health professionals involved in treating and caring for people with HIV, is asking for it in England.
It is currently available for free as part of the Impact study in England, which began in September 2017 and is expected to end in August, but places are limited.
Sexual health consultants say the study is particularly useful for people who can't afford Prep in particular, and among the 15 cases of people who get HIV while waiting for trial sites, several people were on a low income and couldn't afford it. the medicine in another way.
How did this happen?
Pre-exposure prophylaxis pills can be highly successful in protecting a person from HIV.
David, who is 40 and lives in London, is one of the people who got HIV while waiting for a place at the trial.
Unable to pay Prep in particular, he tried to access the pills through two different sexual health clinics in London, but was informed that there were no spaces available in the study.
Just a few weeks after not having access to the drug, he became ill and was eventually diagnosed with HIV.
"I was stunned. It was like & # 39; Oh my God, how did this happen? & # 39;
"Trying at two different clinics to get in touch with him and not be able to get in, and then get HIV – I was very, very angry about that.
"The preparation needs to be readily available to anyone. Yes, there is a cost implication, I understand that – it is a tablet for everyone.
"But that person who gets HIV, the costs are 10 times higher, and that's for life."
Dr. Iain Reeves, chief HIV clinician at Homerton Hospital in East London, says he had to tell three people who were previously HIV negative who had acquired the disease after being unable to access Prep for free from their service.
"Unfortunately, we had no place in the study. We gave them all the information on how they could access it, including online shopping," he said.
"But of course, for many people, this is very difficult if you don't have enough money to buy it online."
The Impact study was expanded earlier this year to meet demand, but London took up only 60% of the extra space offered, which was believed to be due to problems involved in financing increased services.
Dr. Laura Waters of the British HIV Association says Prep must be universally available through the NHS for people at high HIV risk.
"The tension around funding is complicated," says Laura Waters, president of the British HIV Association.
"It's not simple. But the reality is that the NHS England is funding the drug during the trial, but it is the local authorities that fund the sexual health clinics.
"When the Impact study started, we only had branded products available. Now it's available in the unbranded generic version, which is much cheaper. But the reality of creating more sexual health consultations when our funding was cut is a big one." challenge. . "
The BBC has learned that Prep costs the NHS about 11 pounds per person per month. The privately owned Prep starts at about £ 30 a month.
The cost of medication for an HIV positive patient ranges from £ 100 per month to £ 500 per month and needs to be provided for the rest of that person's life.
For those who argue that individuals most at risk for HIV should practice safer sex and use condoms, consultants say as a comparative argument that condoms are not always fully effective in preventing pregnancy and it is a personal choice which form of protection to use.
In addition, they point out that those who receive Prep through clinics have general health checks and are regularly checked for STDs, while those who buy it privately do not have the same orientation.
This means that an individual who is HIV positive but not aware of his or her status can begin taking Prep in particular with the intention of preventing a disease they already have.
In a statement, the NHS England said: "The expansion will help ensure that study learning can fully inform future service planning in partnership with local authorities and protect more people from HIV at the moment."
The Department of Health said plans are underway for a "continuous transition from testing to routine commissioning" when the trial ends next year.
However, HIV experts say they have had no guidance on how this will happen.