A health watchdog has been forced to apologise to dozens of GP practices after statistical errors mistakenly put them in a high concern category.
Some 60 practices which were categorised as being in the highest priority for an inspection have now been moved into lower bands.
A further seven will now be targeted for an early inspection having previously been categorised as a low risk.
The Care Quality Commission (CQC) said it will make a "big apology" to those affected by the changes.
T he CQC launched its "intelligent monitoring" database last month, allowing patients to see which practices were highest on the list of priority for inspections under the watchdog's new regime.
Some 1,200 fell into the top two priority bands, labelled the "highest concern", based on evidence of patient experience, care and treatment from sources including major surveys and official statistics.
Many were rated as either a "risk" or "elevated risk" on a checklist of 38 indicators including poor access to appointments, deficient planning for mental health patients and insufficient cancer screenings.
But a BBC investigation found serious errors in the calculations used by the CQC to assign practices to one of six risk bandings.
The corporation discovered that for one indicator, whether patients were able to get an appointment with a GP or nurse the last time they tried, the calculations were so flawed that the CQC has been forced to remove the indicator altogether.
A further four indicators had to be refined based on revisions to data provided to the CQC by NHS England.
A letter explaining what had happened, sent by Professor Nigel Sparrow, the CQC's s enior national GP advisor, said: "T he vast majority of GP practices will not be affected by these changes.
"Overall, 60 practices (less than 1%) previously in higher priority bands 1 and 2 will now move to bands which are of lower priority for inspection.
"We will contact each of those practices to apologise for any concern this may have caused GPs, their staff and their patients.
"We will also contact the seven practices which will move into a higher priority band as a result of these changes."
He stressed that "banding is not a judgment" and "intelligent monitoring will never be used in isolation to make a final judgment or produce a rating of a GP practice".
Sir Mike Richards, chief inspector of hospitals for the CQC, told the BBC: "We will make them a big apology. This only became apparent when we ran the data on the thousands of practices rather than just the hundreds that we tested them on."
He added: "I wish it hadn't ever happened, yes, obviously. But sometimes these things only come to light when you look at the full number - the 7,660 practices or whatever the number is."
The British Medical Association's GP committee chairman Dr Chaand Nagpaul said: "Today's admission by the CQC that they are having to recalculate all of their pre-inspection data highlights the concerns that the BMA raised that this risk rating system is not fit for purpose.
"We now know that due to errors in the CQC's methodology 60 practices have been unfairly branded as being at risk, potentially doing serious harm to their reputation.
"The chopping and changing of target indicators which has resulted in a different risk banding being allocated to GP practices demonstrates the problems of using limited skewed data, rather than adopting a transparent approach.
"The CQC has also reiterated that these bandings are not a reflection of the quality of care a practice provides, a fact that means the inspection regime could even in its revised state mislead the public. The banding system as a whole needs to be withdrawn.
"We warned at the time that simplistic targets would fail to take into account the enormous pressures GP practices are facing, and that skewed and limited information does not tell us about the quality of care.
"These failings have the potential to seriously undermine the trust in the system and patients' confidence in their GP and it is only right that all of those practices affected are now contacted and receive a full apology."
Maureen Baker, who chairs the Royal College of General Practitioners, said: "This is shocking news, especially for the GP surgeries who have been wrongly labelled and for the patients whose trust in their family doctors has been cruelly shaken.
"It is ironic that a system that was introduced supposedly to support patients has left them confused and let down. The damage caused by this episode will not easily be undone.
"The publication of these over-simplistic bandings has stigmatised hard-working family doctors, who are trying their hardest in very difficult circumstances to provide the very best care for their patients.
"To discover that the data on which these banding decisions were based is severely flawed will further demoralise our hard-pressed GPs and destroy any semblance of confidence that they had in the inspection system.
"We absolutely recognise and support the need to provide transparent, meaningful information to the public about the care provided by their GP practice.
"But we had previously written to the CQC with our concerns that the bandings were flawed and did not take into account the particular characteristics and challenges faced by individual practices.
"Every patient has a right to expect high-quality and consistent care from their local GP practice, and it is crucial that we urgently address any variations in quality of care. But many practices are struggling to meet quality standards due to factors beyond their control, such as lack of funding, significant increases in patient consultations and difficulties in trying to recruit sufficient GPs to meet patients' needs."