The infection of up to 30,000 people with contaminated blood has been called the biggest treatment disaster in NHS history. Thousands have died.
A public inquiry has been taking evidence about the scandal and is due to hear from Health Secretary Matt Hancock.
Who was affected?
People with haemophilia and other bleeding disorders were given blood infected with HIV and hepatitis viruses, during the 1970s and 1980s.
It was the result of a new treatment intended to make their lives better. A clotting agent called Factor VIII was introduced to help their blood to clot.
Before this, patients faced lengthy stays in hospital to have transfusions, even for minor injuries.
People who had blood transfusions after an operation, or childbirth, are also thought to have been exposed.
About 5,000 people are believed to have been infected - but some estimates put the number at 30,000. Nearly 3,000 people have died.
How did it happen?
The UK was struggling to keep up with demand for the Factor VIII blood clotting treatment, so supplies began to be imported from the US.
But much of the human blood plasma used to make it came from donors such as prison inmates and drug-users, who sold their blood.
These groups were at higher risk of blood-borne viruses.
However, at the time, HIV had not been diagnosed and understanding about hepatitis was still developing.
The risk of contamination was raised further because Factor VIII was made by pooling plasma from up to 40,000 donors and concentrating it.
How long did this last?
By the mid-1980s, once it was clear HIV was blood-borne, the products started to be heat-treated, to kill the viruses.
But questions remain about how much was known before this time.
Despite these precautions, some of the contaminated blood products remained in circulation and continued to be used.
Screening of all blood products began in 1991.
And by the late 1990s, synthetic treatments for haemophilia became available, removing the infection risk.
What is the inquiry looking at?
The UK-wide inquiry was launched after years of campaigning by victims, who claim the risks were never explained and the scandal was covered up. It is being led by former judge Sir Brian Langstaff.
One of the first to take the stand in 2019 was Derek Martindale, who has haemophilia. He was 23 when he was diagnosed with HIV and given a year to live, in 1985. He survived but his brother - who was also infected with HIV - did not.
The inquiry has also heard from victims' relatives including Liz Hooper, who lost two husbands, both of whom had been given infected blood.
Health Secretary Matt Hancock is due to give evidence.
"This is the first time a serving [UK] cabinet minister will have given evidence in front of victims and their families," said Su Gorman, whose husband Steve Dymond died aged 62 in December 2018 of organ failure linked to hepatitis C.
Ministers from Wales, Scotland and Northern Ireland have already given evidence.
Financial compensation for the families of victims has been an ongoing question, with UK nations offering different levels.
In March, Cabinet Office minister Penny Mordaunt announced compensation for victims' families in England would be increased, to bring it in line with other parts of the UK.
Have people been infected elsewhere in the world?
There have been thousands of cases of people being given infected blood in the US.
But other countries also imported blood products during the 1970s and 1980s.
In Europe, cases in France, Ireland, Portugal and Italy have been identified. Japan, Canada, Iran and Iraq have also been caught up in the scandal.
In the US, companies that supplied infected products have paid out millions of dollars in out-of-court settlements.
In other countries, politicians and drug companies have been convicted of negligence.
None of that has happened in the UK - although victims have been given limited financial support.
At the opening of the inquiry, it was announced that criminal trials could follow.