Patients are waiting a week longer to see a consultant than four years ago, experts have warned, as they pointed to a "worrying" trend for increasing waiting times.
NHS waiting lists have grown in the past eight years, according to the study from the Nuffield Trust and the Health Foundation, from to 2.35 million people waiting in December 2008 to start treatment led by a consultant, to 3.7 million in September this year.
The Government has also abolished two targets relating to waiting times, and standards have unsurprisingly slipped against these markers, the report's authors said.
Some 77% of admitted hospital patients started treatment within 18 weeks, according to this year's September figures (a nine percentage point drop on June 2015 figures, when the targets were abolished).
Meanwhile, some 90% of non-admitted patients received treatment within 18 weeks (a five percentage point drop on June 2015 figures).
The abolished targets, which were hit between 2008 and 2014, were for 90% of admitted and 95% of non-admitted patients to start treatment within 18 weeks.
Even a newer target, which says 92% of all patients should wait less than 18 weeks to start treatment, has also been mostly missed in 2016, the report said.
Overall, the typical waiting time for patients scheduled for treatment has increased by just over a week, from 5.5 weeks in April 2012 to 6.6 weeks in April 2016.
Experts behind the study said the figures showed a "worrying reversal in waiting times for patients" compared to earlier years.
Their report - which covers England - also found the NHS was performing poorly in other key areas, including the number of people waiting for tests to diagnose them with conditions.
These tests include things such as MRI scans, colonoscopies to look for bowel problems, and hearing tests.
In December 2008, some 403,955 people were waiting for diagnostic tests but this number has now more than doubled. In January this year, 818,599 people were waiting and the figure for September was 882,312.
These figures are set against a rise in the number of tests now being undertaken.
The report also pointed to increasing issues with ambulance response times, with nearly four in 10 ambulances now taking longer than eight minutes to reach life-threatening emergencies.
It also said bed occupancy was at "dangerously high levels", increasing the risk of infections for patients.
The report concluded: "Waiting times for consultant-led treatment, ambulance response times and waiting times for A&E are all areas of concern, with performance against some of these rising to levels not seen since earlier this decade. "
It added: "Waiting longer may mean preventable conditions are not addressed, while delays in treatment can mean minor ailments become bigger problems.
"The considerable pressures under which ambulance services are working and the lengthening waits for ambulances responding to life-threatening situations are deeply worrying."
But the report's authors did point to key areas of improvement across the NHS, including reductions in smoking in pregnancy, better stroke care and improvements in patients' experience of hospital care.
Nigel Edwards, chief executive of the Nuffield Trust, said: "The fact that the financial squeeze didn't immediately affect the quality of patient care reflects the hard work and goodwill of NHS staff.
"But slowing improvement in some areas of quality, combined with longer waiting times and ongoing austerity suggests the NHS is heading for serious problems.
"It seems likely that a system under such immense pressure will be unable, at some point, in some services, to provide care to the standards that patients and staff alike expect."
An NHS England spokesman said: "Last month, more than 1.3 million patients started consultant-led treatment, and more than nine out of 10 patients were waiting less than 18 weeks.
"We're working hard to cut long waits, and the number of patients waiting over a year has dropped from over 5,000 recorded in March 2012 to being just over 1,400 now.
"In the last five years, since March 2011, the NHS has reduced the number of patients waiting more than a year for treatment by just under 13,000."