Mortality figures which led to children's heart surgery being suspended at Leeds General Infirmary appeared to show the number of deaths was twice the national average - but a lead clinician has said the figures were "not fit to be used".
Sir Bruce Keogh, the medical director of NHS England, said the figures were among a "constellation of reasons" to suspend operations, as well "disturbing" calls he received from two whistleblowers.
The hospital, which is at the centre of a long-running row over the future of its children's heart services, is carrying out an internal review after data suggested a death rate twice the national average.
But campaigners criticised the decision and its timing, 24 hours after a High Court judge ruled the decision-making process to close the children's unit was "legally flawed".
Dr John Gibbs, chairman of the steering committee for the Central Cardiology Audit Database (CCAD), which supplied the data, said the mortality figures were preliminary and had not undergone the "usual rigorous checking process".
"I'm absolutely furious," he said. "This data was not fit to looked at by anyone outside the committee.
"It was at a very preliminary stage and we are at the start of a long process to make sure the data was right and the methodology was correct.
"We would be irresponsible if we didn't put in every effort to get the data right."
Dr Gibbs said the "ground-breaking" study involved complex analysis which would require at least two months to validate.
A problem had already been identified with the figures, he added, with some data being incorrectly discounted from results.
The decision to suspend surgery was made yesterday following meetings between senior officials at NHS England and the Care Quality Commission, as well as bosses from Leeds Teaching Hospitals NHS Trust.
Sir Bruce said there were "rumblings" among the cardiac surgical community for some time that "all was not well" in Leeds.
But he admitted the timing of the suspension looked "suspicious", coming a day after the High Court quashed plans to close the unit.
"The trust has taken a highly responsible precautionary step," Sir Bruce said.
"Some questions have been raised by the trust's own mortality data and by other information.
"It is important to understand that while this information raises questions, it does not give us answers.
"But it is absolutely right not to take any risks while these matters are being looked into."
Sir Bruce later told BBC Radio 4's Today programme: "There have been rumblings in the cardiac surgical community for some time that all was not well in Leeds.
"On Tuesday I had two phone calls which I found disturbing, both from highly respected temperate surgeons who commenced the conversations by saying they had to speak out."
One raised concerns about the referrals process at the hospital and the other spoke to him about staffing levels, Sir Bruce said.
He added: "I couldn't do nothing. I was really disturbed about the timing of this. I couldn't sit back just because the timing was inconvenient, awkward or would look suspicious, as it does."
Greg Mulholland, MP for Leeds North West, said he was "stunned and appalled" by the suspension and called for Sir Bruce to resign.
The MP said he understood the medical director of NHS England and senior members of the Care Quality Commission arrived at LGI yesterday morning to demand that children's heart surgery cease.
In a statement on his website, Mulholland said: "To have arrived in Leeds and done this, without warning, just one day after the decision to close the Leeds unit was proved in a court of law to have been unlawful, beggars belief.
"I believe that Sir Bruce Keogh should resign as he has both authorised this wholly unreasonable and deeply questionable action and also presided over the fundamentally flawed Safe and Sustainable review, which has proved an exercise in how not to effect major change to the NHS."
Leeds Central MP Hilary Benn said: "I spoke to Jeremy Hunt this afternoon and stressed to him the importance of maximum openness. The decision to stop operations has come as a great shock to all of us and we need all the facts to be put in the open.
"Sir Bruce Keogh said this morning that the data showed Leeds to have a mortality rate that was twice the national average.
"Now we discover that the person responsible for the data Dr John Gibbs, chairman of the steering committee for the Central Cardiology Audit Database (CCAD), is reported to have said that the mortality figures were preliminary, had not undergone the usual rigorous checking process and were not fit to be looked at by anyone outside the committee.
"The only way to resolve this is for the data - with all the caveats included - to be published immediately so that it can be examined, and I urge the Secretary of State to do so without delay."
Maggie Boyle, chief executive of Leeds Teaching Hospitals NHS Trust, said: "We apologise to parents and families who will be affected during this time, and can assure them we always put the safety of our patients first.
"Families whose surgery may be affected during this time are being contacted directly by the trust."
The Children's Heart Federation said it was "deeply saddened" by the suspension.
Anne Keatley-Clarke, chief executive of the charity, said: "My concern is that it appears that managers and clinicians in Leeds, together with the parent support group, have put their own interests ahead of the well-being of critically ill children and their very vulnerable parents."
A campaign has been waged to save children's heart surgery at the LGI after the unit was earmarked for closure as part of an NHS plan to reorganise services across England into fewer, more specialised centres.
On Wednesday Mrs Justice Nicola Davies allowed a challenge against the Leeds unit closure and declared the decision-making process "legally flawed".
She said there had been "a fundamental unfairness" in the consultation process.
The judge emphasised that she was not ordering that the whole consultation process had to be re-run.