The number of urgent operations being cancelled has risen 27% in two years, new figures show.
Data from NHS England shows 4,093 urgent operations were cancelled in 2016 as the health service came under more intense pressure.
In 2014, the number was 3,216.
NHS trusts have been raising the alarm over problems in the NHS throughout this winter, issuing more than 200 crisis alerts a week and having to divert patients from too-full A&E departments.
Figures for the week ending January 22 show 43 NHS trusts put A&E diverts in place, down from 52 the previous week but more than double the same period last year.
Some 51 trusts had at least one day during the week when they had to raise the alarm - called an operational alert - with some saying patient care may be compromised.
This is down from 68 the previous week, suggesting pressure in some areas is easing.
NHS England and Public Health England said flu cases were a worry, together with issues caused by the continuing cold weather.
There were 11 deaths from flu during the week and 65 people with flu needing intensive care or high dependency care.
There have been 53 deaths from flu so far this winter.
An NHS England spokesman said: "With seasonal flu on the rise, if you're otherwise fit and healthy, there's usually no need to see a doctor if you have flu-like symptoms. The best remedy is to rest at home, keep warm and drink plenty of water to avoid dehydration."
Norovirus, which causes diarrhoea and vomiting, also continues to be reported at higher levels in hospitals than the same time last year.
The figures on cancelled operations are the highest on record.
Shadow health secretary Jonathan Ashworth said: "Theresa May's NHS crisis continues, and the problems are worse and more widespread than in previous years. By underfunding and overstretching the NHS, the Tories have pushed health services to the brink.
"Even urgent operations are now being cancelled in record numbers - 4,093 in 2016, up 27% in just two years.
"The Prime Minister needs to explain what she's going to do to fix this mess - not just pass the buck to local health providers. Cuts to social care have left patients stuck in hospitals across the country even when they are ready to leave, with knock-on effects for those waiting for treatment.
"Urgent action is required and Labour are calling for a sustainable health and social care package to be brought forward in the March Budget, so that the NHS and its patients never have to go through a winter like this again."