Row over ambulance times rages on
Ambulance services said proposed changes to response times would benefit all patients as a row continued to rage over the plans.
Labour attacked Health Secretary Jeremy Hunt, demanding more information and claiming he had treated Parliament with contempt.
The Department of Health said "no decisions have been made" and Mr Hunt would only agree to plans that improve response times for the most urgent cases.
A leaked document, obtained by the Press Association, included plans to change the response time for some "Red 2" patients - those with "serious but not the most life-threatening" conditions - from eight to 19 minutes in England.
It said the proposals have been approved by Mr Hunt, subject to confirmation from the medical directors of 10 ambulance trusts.
The current target is for an emergency vehicle to reach those in life-threatening situations within eight minutes.
According to the leaked memo, drawn up by the Association of Ambulance Chief Executives (AACE), NHS England has agreed "in principle" to relax the maximum wait for some Red 2 incidents, which include a range of serious problems including strokes and seizures.
The only higher category is Red 1 - "immediately life-threatening" incidents such as cardiac arrest, choking and major bleeding.
The changes would see about 40% of Red 2 incidents move to a 19-minute response target while the proposed date for implementing the plans is the first week of January.
The AACE said in a statement that plans for change would improve the care provided to the most seriously ill and injured patients and release resources which would be used to improve ambulance waiting times for all.
It added: "AACE supports the plans, which have been developing over the last 18 months, and medical directors of all 10 ambulance trusts in England have been closely involved in their development.
"They will expand the number and type of calls that come into the most serious category (Red 1) so that those who have life-threatening emergencies get an even faster response than is currently enjoyed.
"In addition, they will allow us to ensure that only those patients who truly need a response in eight minutes receive one."
And it said: "At this stage, these are only proposals and they will not be formally approved until NHS England and the Secretary of State are convinced, as we are, that they are clinically safe and that they offer better care for our patients.
"We have been surprised by some of the reaction today given that over the last three months the principles of what we are proposing and the benefits for patients that we envisage have been shared with Labour, Conservative and Liberal Democrats and we have received no negative feedback on the thrust of those principles."
A Labour spokesman said: "We have never given any support for this plan. When raised in passing, (shadow health secretary) Andy Burnham explicitly warned of the need for caution and consultation.
"The evidence needed to be produced first and it hasn't been. Instead, ministers are forcing it through from January, in the middle of a crisis, without proper planning."
Mr Burnham wrote to Mr Hunt today to demand immediate answers on the plans and ask why Parliament was "treated with contempt" three days after he signed them.
He said: "Jeremy Hunt was dragged before Parliament last Thursday to answer questions on NHS winter planning but treated it with contempt.
"It is outrageous that he decided to keep MPs and the public in the dark about a decision he had already taken and one which will have far-reaching implications across the NHS.
"Patients are already waiting hours on end for ambulances to arrive. People will struggle to understand how, in the middle of a crisis, it makes sense for the Government to make a panic decision to relax 999 standards and leave patients waiting even longer."
A Department of Health spokesman said: "We have given ambulances an extra £50 million this winter to ensure the service remains sustainable and the Secretary of State agreed that NHS England should investigate a proposal from the ambulance services themselves to see whether the service they offer the public could be improved.
"No decisions have been made and the Secretary of State would only agree to proposed changes that improve response times for urgent cases."
Professor Keith Willett, trauma surgeon and head of NHS acute care, said: "Any operational changes to ensure ambulances reach sickest patients even quicker would need to be proposed by the senior doctors running ambulance services and agreed by the NHS nationally.
"No such decisions have been taken on their proposals, nor will they be - one way or the other - until next year."