A political row has broken out after a leaked report suggested target times for ambulances to reach some seriously-ill patients - including those suffering a stroke - could be lengthened.
The document, obtained by the Press Association, includes 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 Health Secretary Jeremy Hunt, subject to confirmation from the medical directors of 10 ambulance trusts.
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.
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, NHS England has agreed "in principle" to relax the maximum ambulance 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 report states.
Andy Burnham, Labour's shadow health secretary, said: "This has all the hallmarks of a panic move and suggests Jeremy Hunt's only solution to the A&E crisis is to give up and move the goalposts.
"Rather than getting ambulance response times back up to established standards, it looks like he is running up the white flag.
"The situation in the NHS is now serious and Jeremy Hunt is failing to provide the leadership it desperately needs.
"While there may be a case for reviewing these rules, this is not the way to do it.
"It is nothing short of dangerous to make a snap decision at the start of the most difficult winter in the NHS for years."
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."
Mr Hunt tweeted about the Mail on Sunday's front page headline about the proposals – "Secret plan to double ambulance wait times".
He posted: "Categorically refute scaremongering MoS headline – no plans to double ambulance waiting times, and there never have been."
