A health service manager claims he was gagged by the NHS from speaking out about his dismissal and his concerns over patient safety.
Gary Walker said he had no choice but to sign an agreement linked to a confidentiality clause in April 2011.
He said it was a case of either signing the so-called "super gag" agreement or losing his house.
Nearly two years on, Mr Walker is the first former NHS employee to break the gag.
He has decided to speak out about his concerns over patient safety and the circumstances leading to his sacking from the NHS.
It comes a week after Robert Francis QC, who led the public inquiry into the Stafford hospital scandal, demanded that such agreements should be "banned".
In an exclusive interview for BBC Radio 4's Today programme, Mr Walker, 42, explained his reasons for reluctantly signing the agreement.
He said: "I was in danger of losing my house - I have children to support. And one thing you must remember that if you're attacking the very top of the NHS the sanctions are pretty dramatic.
"So I spent 20 years in the health service and I'm blacklisted from it. I can't work in the health service again."
In early 2010, Mr Walker was sacked as chief executive of the United Lincolnshire Hospitals Trust (ULHT) on grounds of "gross professional misconduct" for allegedly swearing in a meeting.
He and former trust board members claim the real reason lay in his refusal to hit Whitehall targets for non-emergency patients.
Mr Walker says demand for emergency hospital beds in 2008 and 2009 became so acute that he felt he had no other choice than to abandon the 18-week Whitehall target for non-emergency cases.
ULHT is one of 14 hospitals in England currently being investigated for high deaths rates, in the wake of the Stafford hospital scandal, where hundreds are believed to have died after receiving poor care.
He said: "It's a simple decision: you have emergency care or you have care that could wait.
"It's not nice to wait but it could wait and therefore we chose as a board - it was not just me - that we should take priority - that emergency care should take priority."
Mr Walker warned senior civil servants that he faced the same dilemma that led to disaster in Mid Staffs.
But he claims that his immediate bosses at the East Midlands Strategic Health Authority (SHA) instructed him to hit the targets "whatever the demand" and then ordered him to resign when he refused to back down.
A spokesman for the SHA said it "totally refuted" Mr Walker's allegations, describing them as "unfounded". The spokesman said the SHA had always acted "appropriately and properly" in the "interest of patients".
He added: "The SHA... initiated an investigation in April 2009 which looked at quality and safety in the Trust. A number of senior doctors and nurses formed part of the review team which interviewed patients and visitors, as well as a range of Trust clinical and managerial staff.
"The review confirmed that there appeared to be a lack of strategic direction at the Trust and that clinical governance arrangements were weak.
"The SHA worked closely throughout that period with commissioners and key regulatory bodies, but in the final analysis, the SHA had to take action in order to assure quality care for patients."
Mr Walker said the Trust board supported his stand and refusal to back down. Under a replacement chairman, Mr Walker was dismissed in 2010 for swearing in meetings.
Mr Walker and his supporters described this as a "trumped up charge".
Mr Walker said: "One of the witnesses was a senior trade union officer who was present at the meeting and disagrees that my conduct was such that deserved anything like the sanction that was offered.
"You have to remember that if you work in the NHS and you cross the people in power there will be consequences for you and people are appointed to do specific jobs of getting rid of people.
"I think if you consider that had they got a case against me that was reasonable and it was gross misconduct then why would they spend so much time, effort and money to silence me?"
Mr Walker claimed wrongful dismissal, but his employers, the NHS Trust, agreed a compromise agreement with Mr Walker in April 2011.
The Department of Health is cited in the agreement as an "associated person" - one of the NHS bodies to benefit from the agreement and its confidentiality clauses prohibiting Mr Walker from disclosing his £500,000 pay-off or even the existence of the agreement itself.
Mr Walker added: "This is wider than just unlawful compromise agreements. This is a culture that's driven by the top. This is a culture of fear, a culture of oppression - of information that's either going to embarrass a civil servant or embarrass a minister.
"These are big problems. And if you consider that the people that have been running the NHS have created that culture of fear, they need either to be held to account or new people need to be brought in to change that culture."
Mr Walker claimed the use of the super gag is widespread within the NHS.
He said: "I don't see whistle-blowers being protected in the NHS at all. I know dozens of people who I can't even talk to you about who because they are gagged, who are senior people - doctors, consultants - who cannot speak out.
"So I don't believe that there's protection in the health service. I believe that there are pockets where whistleblowers are welcome but on the whole if you're going to bring bad news you are going to be asked to step aside."
Following the recording of his interview with the Today programme, Mr Walker received a letter from solicitors representing the United Lincolnshire Hospitals Trust.
The note from lawyers DAC Beachcroft said: "Having seen an outline of the issues, we have advised our client that if you have provided an interview or should this interview proceed you will be in clear breach of the agreement and as a result the Trust would be entitled to recover from you the payments made under the agreement and any costs including its legal costs."
Mr Walker has dismissed the note as a "threat".
In a statement, the Department of Health said: "The government has taken a series of steps to encourage an open dialogue, including changing the NHS Constitution to enshrine the fact that NHS organisations should support staff who raise concerns, ensure those concerns are fully investigated and ensure that there is someone independent, outside of their team, to speak to.
"That change also set out a legal right for staff to raise concerns about safety, malpractice or other wrongdoing without suffering any detriment.
"We have consistently made clear to the NHS that local policies should prohibit the inclusion of confidentiality "gagging" clauses in contracts of employment and compromise agreements which seek to prevent the disclosure of information which is in the public interest.
"Sir David Nicholson has also written to NHS organisations reminding them of their responsibilities in relation to compromise agreements.
"As we made clear in our initial response to the Francis Inquiry last week, the culture in the NHS needs to change and high quality patient care must be paramount."
The Chair of the Health Select Committee Stephen Dorrell said legal action should be taken against any senior NHS employee who suppresses information relating to patients' safety.
He said: "If any individual takes that kind of action that should be a criminal offence; it would be a new criminal offence, you can't do this retrospectively, but we should introduce a criminal sanction to prevent people suppressing information of this kind."