Just over 85% of people attending A&E departments in the UK in January were seen within four hours, the lowest since records began.
The figure is also 10% lower than the 95% target set by the government, which has not been hit since July 2015.
According to figures released by NHS England, 85.1% of patients were seen within four hours in all A&E departments in January, lower than 88.7% for December.
For the 2016-17 financial year so far, 89.2% of patients were seen within four hours, down from 92.8% at the same point in the 2015-16 financial year.
Elsewhere, there were 79,500 patients who were delayed more than four hours from a decision to admit to admission, an increase of 54.2% higher from 51,600 for the same month last year.
There was also an a total of 988 patients spending more than 12 hours from a decision to admit to admission in NHS hospitals compared to 158 in January 2016.
The monthly performance figures are the worst since records began in 2010.
Health Secretary Jeremy Hunt has urged NHS hospitals to show improvement in hitting the four-hour A&E waiting time target and insists the target will be hit in March 2018 following the injection of funding following the 2017 Spring Budget.
Chancellor Philip Hammond announced there will be an additional £2bn for social care in the UK during his first Budget speech in the House of Commons, adding the Tories are the "government of the NHS".
Jonathan Ashworth MP, Labour's Shadow Health Secretary, described the figures as a "damning indictment of Theresa May's neglect of our NHS."
He added: "The Tories are overseeing a startling collapse in standards and Theresa May is still in complete denial as to the sheer scale of the crisis. Jeremy Hunt must be clearer about what action he's going to take to make sure patients and their families never have to go through a winter like this again."