Labour's plan to reduce NHS waiting times to only 18 weeks is unlikely to work, health service bosses have said.
The majority of hospital and ambulance chief executives have said the NHS will not be able to meet the Government's pledge to reduce waits for hospital appointments to 18 weeks within the current Parliament.
The backlog stands at 7.64 million and the target of seeing 92 per cent of patients within 18 weeks of a referral has not been met since 2016.
The NHS Providers' annual State of the Provider Sector survey, which included responses from 171 NHS leaders from 118 hospital, acute specialist and ambulance trusts in England, revealed that most thought it was "unlikely" or "very unlikely" this would be achieved.
While 71 per cent of trust bosses did not think Labour's pledge would be met within five years, this increased to 100 per cent among leaders from acute specialist and ambulance trusts.
Currently more than a quarter of a million patients have been waiting longer than a year for an appointment or procedure, according to the latest data, and more than 3,300 had been waiting for at least 18 months.
Labour's plans to cut the backlog involve putting on an extra two million appointments a year.
But NHS bosses warned there was a "fundamental mismatch" between demand for services and what the NHS is able to do.
The leader of one NHS trust said: "The Government has got the most focus on getting back to 18 weeks, which is the hardest standard to meet of all.
"If you think, there were seven million people on a waiting list, and as fast as you take them off, currently, we're putting more people on.
"So that is a huge numbers game that's going to cost a huge amount of money, unless you can do something to arrest the increase of people going on to waiting lists.
"If you don't create the capacity in primary care, in children's services, in mental health, you can't do the management of people properly in the community and stop them getting so acutely unwell."
Saffron Cordery, the deputy chief executive of NHS Providers, said: "There will be progress, but can trust leaders, with hand on heart, say that they're going to meet that 18-week standard? I think that is really difficult and challenging to predict."
The survey also found 79 per cent of trust leaders are either worried or very worried about meeting demand for services over the next year, a similar proportion to 12 months ago, but higher than the 61 per cent reported before the pandemic.
The Government has said its 10-year plan for the health service, which will be published next spring, will include shifting more care from hospitals into community services.
In the Budget, Rachel Reeves, the Chancellor, described the £22.6 billion increase in the day-to-day health budget over two years as a "down payment" on the 10-year plan.
She said it would "bring waiting lists down more quickly" and towards the 18-week target.
Ms Cordery said the funding "needs to cover significant costs", a number of which had already been allocated for the current year, including pay rises for NHS staff.
"In terms of the Budget allocation, what we do know is that much of it is already allocated. And I think that's going to be one of the challenges," she said.
"The big 22-plus billion pounds is across two years and then, when you drill into that, it needs to cover significant costs that are already allocated.
"So that includes pay rises, which are going to eat into that significantly.
"In terms of those allocations, I think they're big numbers, they're welcome numbers, but, in terms of outgoings already slated, we know that they're not going to go that far."
Ms Cordery also touched on the rise in employers' National Insurance contributions announced in the Budget amid concerns the change could affect GPs, hospices and care homes.
"We know that the National Insurance contributions are going to be covered for NHS services, but beyond that we genuinely don't know what's going to happen," she said.
One trust leader described the "real tough financial conditions of our local government partners" and warned the Budget will add to problems for some services.
They added: "Given that they have to balance their books every year, because it's their statutory responsibility, they are finding it really challenging, and I think the new Budget will be even harder for them, especially if care homes and domiciled agencies have to incur the NI costs that they have at the moment - that's only going to increase problems in the sector."
Karin Smyth, the Health Minister, said: "We inherited an NHS that is broken, but we are fixing the foundations with a nearly £26 billion boost for the NHS over this year and next.
"We've already eliminated A&E strikes, making this the first winter in three years that all A&E staff will be on the front line, not the picket line, and we're working with trusts to make sure the system is prepared for what is always a challenging period.
"Through our 10 Year Health Plan we will build an NHS that is fit for the future and delivers for patients all year round, as we work towards our commitment to ensuring patients can expect to be treated within 18 weeks."