Theresa May has announced a wide-ranging inquiry into the contaminated blood “scandal” of the 1970s and 1980s which left 2,400 people dead.

The Prime Minister said the treatment of thousands of haemophiliacs and other patients with blood products infected with hepatitis C and HIV was an “appalling tragedy” which should never have happened.

“Thousands of patients expected the world-class care our NHS is famous for, but they were failed,” she said in a statement.

“At least 2,400 people died and thousands more were exposed to Hepatitis C and HIV, with life-changing consequences.

“The victims and their families who have suffered so much pain and hardship deserve answers as to how this could possibly have happened.

“While this Government has invested record amounts to support the victims, they have been denied those answers for too long and I want to put that right.”

The announcement was welcomed by campaigners who have been pressing for years for an inquiry into the import of the clotting agent Factor VIII from the US.

Much of the plasma used to make the product came from donors like prison inmates who sold their blood which turned out to be infected.

Greater Manchester Mayor Andy Burnham – who as shadow home secretary championed the campaign for an inquiry – said the announcement was a “major breakthrough”, albeit a belated one for people who had suffered for decades.

“This day has taken far too long in coming. People have suffered enough through contaminated blood. They have been let down by all political parties and public bodies,” he said.

“It is now incumbent on those organisations to work together to give the families truth, justice and accountability without any further delay or obstruction.

“It is essential that this inquiry looks at both the original negligence and the widespread cover-up that followed.

“It is also crucial that organisations representing victims are fully consulted on the form, membership and structure of the inquiry.

“Just as with Hillsborough, there must be a ‘families first’ approach at all times.”

The announcement came just two days after six party leaders in the Commons – including Labour leader Jeremy Corbyn and the Democratic Unionists’ Nigel Dodds – signed a joint letter calling for an inquiry.

Welcoming the move, Mr Corbyn said the investigation should have the potential to trigger prosecutions.

“It was obviously a serious systemic failure. I think we need the strongest possible inquiry that can if necessary lead to prosecution actions as a result, but above all get to the bottom of it,” he said.

“A broad, public, inquisitive inquiry is very important.”

Downing Street said it would now open discussions with those affected as to exactly what form the inquiry would take.

“Consultation will now take place with those affected to decide exactly what form the inquiry will take, such as a Hillsborough-style independent panel or a judge-led statutory inquiry,” the Prime Minister’s official spokesman said.