The lawyer at the centre of an international blood contamination scandal said an inquiry into how it started is the “biggest this country has ever seen”.

Des Collins, founder and senior partner at Collins Solicitors in Watford, said the circumstances surrounding the long-awaited public inquiry begun last week were a “travesty of justice” – and the full extent of which is “completely unknown”.

Mr Collins, 70, and his firm, currently represent around 1,200 people affected by contaminated blood products used by the NHS in the early 1970s that were imported from the United States for patients with haemophilia.

At the time, the US paid for blood donations and accepted them from high-risk groups, such as prisoners, drug users and sex workers.

Thousands were infected with HIV and Hepatitis C right through to the 1990s by blood products designed to help them, but in which many died.

Shortly after the public inquiry began, victims took to the stand for the first time in four decades to express stories of stigma, disease and “disintegration”.

As many as 25,000 people in the UK could have contracted HIV or Hepatitis C as a result of the error. Theresa May announced an annual increase in payments to victims of £75 million.

Mr Collins chose to legally represent the families of those affected after being approached by two victims in 2017.

He said: “I was at the House of Commons at a meeting of people in long standing litigation that wasn’t getting the results they wanted.

“A number of cases were aired one of which was Jason Evans’s whose father had died from AIDS after being given contaminated Factor VIII – a imported plasma derived medicinal product. And I thought surely I cannot be hearing this right.”

Mr Collins invited Mr Evans and another campaigner named Max (not his real name) who had been infected with both HIV and Hepatitis C to his Watford office to discuss their cases.

“Jason started talking, we listened, and four hours later we were totally convinced there was the possibility of us achieving something.”

Collins Solicitors began representing Max and Mr Evans and in the following weeks a “flood” of enquiries from other victims came to his office.

“I think it’s appalling, a travesty of justice,” he said. “The more you look into it the more it becomes obvious it went completely wrong at its conception and mistakes were made by the Department for Health at the outset.

“It is quite obvious the approach taken was wrong and the department should have put its hands up and said, ‘we got it wrong’ and then put it right.”

He added: “And once Factor VIII was a worldwide product it started to go badly wrong. The pharma companies will have to stand up and be counted at this inquiry.”

Mr Collins doubts whether the full extent of the blood contamination will ever come to light – but was unequivocal in saying: “It’s the biggest public inquiry this country has ever seen.”

He added: “It’s a matter of trying to stand back. The families throughout that time disintegrated and fell apart.

“They were aspirational, their lives were ahead of them, life would be good.

“But as the families moved through the years the impact was appalling. It led to suicides.

“It’s not one story. Those families are still broken up and it’ll take a generation to get over it.

“This inquiry will be cathartic and enable people to hopefully put it behind them.”

A department of health and social care spokesperson said: "The infected blood scandal was a tragedy that should never have happened, and the ongoing public inquiry was set up to get to the truth and give families the answers they deserve. We are following the inquiry closely and will continue to cooperate fully."