The Nuffield Trust said the record size of the NHS waiting list across England shows the health service has been set back years by the coronavirus pandemic and now faces a "major backlog".
NHS rules state that patients referred for non-urgent consultant-led elective care should start treatment within 18 weeks.
But NHS statistics show 2,579 patients listed for elective operations or treatment at York Teaching Hospital NHS Foundation Trust at the end of February had been waiting for at least a year – 9 per cent of all those on the waiting list.
This was a huge increase from none the year before, and the highest figure for the month of February since comparable records began in 2012.
The number of people waiting this long across England has risen to 387,900 – the highest total since December 2007, and almost 250 times that of February 2020.
The Nuffield Trust said the strain of the backlog on patients should not be underestimated, but added it is no surprise given the intense pressure of Covid-19 hospitalisations.
Sarah Scobie, deputy director of research at the organisation, said healthcare staff have made huge sacrifices during the pandemic, but more will be asked of them.
She added: “It is clear that the NHS has been set back years as it faces a battle to clear these major backlogs of postponed care.
"Returning to the levels of activity seen before March last year will not be enough to meet demand, and we will continue to live with coronavirus for years to come."
Overall, 27,189 people were waiting to start hospital treatment at York Teaching Hospital Trust at the end of February – an increase of 40 on January.
Across England, 4.7 million people were waiting for treatment at this time – the highest number since records began in mid-2007.
This was up from 4.6 million in January, and means almost half a million patients have been added to the waiting list since the pandemic began in March 2020.
The King's Fund said long waiting times do not just affect patients, with concerns growing over access to community services and mental health provision.
David Maguire, senior analyst at the think-tank, said: "The Government needs to be honest with the public and start planning for long-term NHS recovery.
"A good place to start would be with a fully funded workforce strategy to address the persistent staff shortages that have dogged the service for years."
Prime Minister Boris Johnson said the Government will ensure the NHS has the funds it needs to tackle the build-up in waiting lists.
Professor Stephen Powis, NHS national medical director, said treating 400,000 patients with Covid-19 has "inevitably" impacted the NHS, but the dedication of staff means they delivered almost a million operations and procedures during the winter wave.