There will be a full public inquiry into the scandal-hit Stafford Hospital, the government has announced.
The Tories had promised the probe in opposition after reviews had criticised "appalling" standards which were said to have caused needless deaths.
Campaigners consistently said it was the only way to uncover the failings, but previous ministers had resisted.
Health Secretary Andrew Lansley said the families of those who had died deserved to know how it had happened.
The problems at Stafford - run by the Mid Staffordshire NHS Trust - were laid bare by the NHS regulator in March 2009.
The Healthcare Commission reported there had been at least 400 more deaths than expected between 2005 and 2008.
It cited a catalogue of poor standards, including cases where receptionists had been used to assess emergency patients.
But this was just one of a long-line of reviews.
These included an independent inquiry launched by the government. It was held in private and reported in February, saying the trust had become driven by targets and cost-cutting.
Campaigners believe the failings of Stafford go much further than one badly-run trust however.
The trust had been climbing the NHS ratings ladder during the period in question and was even given elite foundation trust status.
So earlier this year the Labour government set up a further inquiry looking at the role of the wider regulatory agencies, but this was not enough for campaigners.
They demanded a more wide-ranging probe which had tougher powers. A public inquiry is held in open and is able to compel witnesses attend hearings and cross examine them.
Mr Lansley said: "We know only too well what happened at Mid-Staffordshire, in all its harrowing detail, and the failings of the trust itself.
"But we are still little closer to understanding how it was allowed to happen by the wider system.
"The families of those patients who suffered so dreadfully deserve to know.
"And so too does every NHS patient in this country.
"This was a failure of the trust first and foremost, but it was also a national failure of the regulatory and supervisory system who should have secured the quality and safety of patient care."
The inquiry will be chaired by Robert Francis QC who had led the government inquiry and was asked to do the same for the follow up one.
Mr Lansley said he did not want Mr Francis to go over the ground already covered, but focus instead on how the culture in the NHS allowed this to happen.
The final report is expected in March 2011.
The health secretary also said he wanted to strengthen the ability of staff to whistleblow.
He said he would be issuing guidance to trusts on their procedures as well as looking to introduce a contractual right for staff to raise concerns that are in the public interest.
Julie Bailey, founder of Cure the NHS, the campaign group set up by the families of victims, said: "A year ago David Cameron promised a public inquiry and he's kept that promise.
"The terms of reference and scope are just what we wanted.
"Former health ministers, Department of Health executives in Whitehall and in Stafordshire will now have to exlain why they did not stop this disaster."