Ambulance trusts are able to hit response time targets if equipment is nearby to re-start hearts - even if that is useless to the patient.
NHS England rules say trusts can hit targets if a trained person is on the scene and able to use a defibrillator, which is for cardiac arrests.
Trusts can hit the target even if the defibrillator is never used and is actually useless to the patient because they are ill with something else.
The ambulance trust at the centre of a major scandal to deliberately delay ambulances said trusts actually "interpret" those rules to mean just having a defibrillator nearby is enough to count as meeting the response time.
A spokeswoman for the South East Coast Ambulance Service NHS Foundation Trust (Secamb) said NHS trusts up and down the country say they are hitting targets even if no person is trained to use defibrillators.
There have been reports of trusts buying defibrillators just to meet the target.
Secamb uses a web-based map to see if defibrillators happen to be nearby and then retrospectively counts thousands of calls as having hit response-time targets.
The classification of such calls as achieved within eight minutes helped Secamb towards the NHS target of responding to 75% of "life-threatening" cases within eight minutes.
Without this, the trust would have missed the target.
But a spokesman for NHS England said that, for a response to be legitimate and "stop the clock", a fully-trained person (able to use a defibrillator) and a defibrillator have to be on scene.
NHS England said it would not support stopping the clock for a person who happens to be in the vicinity of a defibrillator. No fully-trained person may be present and the defibrillator may not be "on the scene", it said.
It said the definition of a public access defibrillator being "on scene" is that the defibrillator and the person able to use it are at the patient's side.
The spokesman added: "The guidance should be adhered to in letter and in spirit. We support greater training for the public, the use of community first responders and similar schemes, and also the placement of public access defibrillators in accessible locations.
"The presence of a trained individual and a defibrillator at the scene of a cardiac arrest as quickly as possible saves lives and is the principle underpinning this guidance."
A paramedic whistleblower told the Daily Telegraph that Secamb had reported calls as meeting the eight-minute target, regardless of whether the patient was seen by a professional.
They said Secamb reported hitting the target if the defibrillator was was within 250 metres of the patient.
Secamb said the Association of Ambulance Chief Executives (AACE) provided guidance on "interpretation" of the NHS England rules so they were applied consistently.
A spokeswoman said trusts interpreted the rule which says public access defibrillators should have a "fully-trained individual present, at the incident location" according to a "clarification" from AACE.
This AACE guidance says: "Community public access defibrillators by their nature are for use by bystanders who do not have previous training.
"When the initial Department of Health guidance for 'what stops the clock' was originally written, defibrillators required someone trained to operate them.
"With the new generation of intelligent and automatic defibrillators, untrained members of the public can follow the instructions or be guided by control staff to use the equipment.
"Community public access defibrillators are those where the person potentially using them has no training from the ambulance service until the incident occurs."
Secamb is already under investigation for deliberately delaying thousands of "life-threatening" calls which came to it via 111.
Regulators are trying to establish the extent of the harm to up to 20,000 patients.
So far, they have been unable to pinpoint which senior managers made key decisions.
The Patients Association has called an investigation by NHS England into the scandal a "whitewash".