Men who have sex with men are barred from giving blood in England, Scotland and Wales for three months after sexual activity - but some are deciding to break the rules.
"It galls me every time I hear an advert on the radio asking for people to give blood, when there's a huge section of society that is just denied that for no good reason," says David - not his real name.
He is a sexually active gay man who donates blood to the NHS several times a year.
"I grew up in a family who gave blood regularly and instilled in me that that was the right thing to do," he tells the BBC's Victoria Derbyshire programme.
"I did it before I started having sex with men - and I carried on doing it afterwards because, for me, that was the right thing to do."
In 2017, rules were relaxed in England, Scotland and Wales to allow men who have sex with men to give blood after abstaining from sexual activity for three months.
Previously, they had to wait a year - which remains the case in Northern Ireland.
NHS Blood and Transplant - the organisation that looks after blood in England - says the timeframe exists because, while all donations are screened, "there is a period of time following contact with any infection when it would not be detected by our screening tests".
The Advisory Committee on the Safety of Blood, Tissues and Organs (SaBTO) - which advises UK health departments - recommended the changes after concluding new testing systems were accurate and donors were good at complying with the rules.
It followed campaigning from LGBT organisations. But for some, it is still not enough.
David says the law remains "rooted in deep homophobia".
"I don't see why I should be denied the rights to help fellow people," he says.
"Certainly I don't think the people whose lives I've potentially saved would complain."
Asked why he takes the risk, knowing medical professionals believe it unsafe, he says he practises safe sex and is tested more frequently than heterosexual people.
"No straight person I know goes and gets checked every six months," he says.
David, like other men the programme spoke to that knowingly breach the rules, says he takes the Prep drug every day - which can prevent users from contracting HIV.
However, SaBTO's guidelines says those who have used PrEP within the previous three months cannot be accepted because of concerns about how it might impact on HIV screening results.
Su Brailsford, a consultant in health protection at NHS Blood and Transplant (NHSBT), says it is "very concerned" by the programme's findings.
Donating before three months is not illegal and while the NHSBT does have strategies in place to protect blood supply, it cannot currently stop people such as David donating if they lie during donor health checks.
Ms Brailsford says: "The safety of the seriously ill people who receive blood is our number one priority.
"Blood donation exists for patients, not for blood donors.
"Anyone can acquire a blood-borne infection or a sexually transmitted disease but some people have an increased risk of exposure.
"At a population level, men who have sex with men have a higher risk.
"Using protection like a condoms or Prep can reduce this risk but may not eliminate it.
"We have to consider not only the donor but also the potential risks of their partner."
"All donors have to complete the donor health check when they come to donate - so it's not just men who have sex with men who we ask about what sort of sex they've been having."
The facts around blood donation
- NHS Blood and Transplant needs 1.4 million units of blood each year to meet the needs of patients across England - more than 6,000 blood donations per day
- Some 210,000 new blood donors each year are required to replace those who stop donating and to ensure the right mix of blood groups
- The number of men giving blood has dropped by 24.8% over the past five years in England, while the number of women giving blood has fallen by 6%
- Some 40,000 more black donors are needed in England, as they are more likely to have the blood type needed to treat the increasing number of patients with sickle cell disease
Source: NHS Blood and Transplant
The safety of the UK's blood supply has recently been in the spotlight.
Families have been giving evidence in an inquiry examining why thousands of people in the 1970s and 80s were given infected blood products from high-risk sources - with many contracting hepatitis B or C or HIV.
But times have changed and blood screening has improved, leading many to suggest the three-month wait to donate should be reduced further.
The campaign group Freedom to Donate campaigns on this issue.
But for the charity's Ethan Spibey, "it's not helpful" for individuals to break the rules.
Ryan - not his real name - has been donating blood, against the rules, for nearly 10 years.
He says the rules makes him feel he is not good enough and his blood does not matter.
"It's not nice that you're almost discriminated against and you know that you are doing something that you shouldn't be doing," he says.
"But at the same time, morally, you are helping somebody else by giving blood."
Ryan gives blood after promising his mother he would continue to medically donate whatever he could, shortly before she suddenly died.
He says he would not consider abstaining from sex in order to give blood and he takes precautions over his sexual health.
Asked whether he was worried other people giving blood would not be as careful, he said there would always be a risk - including with heterosexuals.
"How many heterosexual people have sex without contraceptive devices or condoms or anything? How much risk are they taking?" he asks.
"I don't think that who I choose to have sexual relations with, or fall in love with, should have any bearing on giving blood."