Total waiting more than 18 weeks for treatment has risen by 43% since coalition came to power

The number of patients not being treated within the NHS waiting-time limit has soared by 43% since the coalition took office, official figures show.

Department of Health data confirmed a large increase in the number of patients who have been denied the right to be treated within 18 weeks, which is enshrined in the NHS constitution.

In May 2010, the month the government came to power, 20,662 of the patients who received NHS-funded treatment in England had waited more than 18 weeks. In November 2011 that number reached 29,508 – a jump of 42.8%.

A rise of 13.9% was recorded in the last year alone, from 25,903 in November 2010 to 29,508 in November 2011. The increases are disclosed in the latest monthly data covering the NHS's Referral to Treatment stipulation that patients should have treatment, which is often surgery, within 18 weeks of being referred by their GP.

The number of patients forced to wait at least a year before being treated has also rocketed under the coalition. In May 2010, 321 of those treated had waited that long, but in November 2011 1,018 had done so – a 217% increase.

The revelations, which cast serious doubt on David Cameron'spersonal pledge to keep patient waiting times low, come on a day when the government is being assailed by a host of medical organisations over its controversial health and social care bill. The prime minister made that one of his five "personal pledges" on the NHS during the "pause" in the bill's parliamentary progress last year.

Labour claimed Cameron had thrown away its achievement of keeping waiting times manageable by allowing the health secretary, Andrew Lansley, to relax NHS targets.

"On what is already a difficult day for the government we now have yet another sign that the NHS is slipping backwards," said Andy Burnham, the shadow health secretary.

"It bears out [the Royal College of Nursing leader] Peter Carter's concerns about an NHS struggling to cope with the chaos inflicted on it by the government. This is exactly what we warned would happen when they relaxed Labour's targets.

"Labour left waiting times at an historic low, but David Cameron has thrown all this away. Sadly, things will get even worse if he succeeds in allowing hospitals to fill 49% of NHS hospital beds with private patients."

In another sign of the NHS's increasing inability to meet its showpiece waiting-time target, the number of primary care trusts (PCTs) not treating 90% of patients within 18 weeks has risen sharply during the coalition's time in office. In May 2010, 18 trusts breached that threshold. But in November 2010 the number was 26 and last November it had risen to 47 – up 80% year-on-year and more than double the number when Labour were in power.

Three PCTs did not treat 75% of patients within 18 weeks in November 2011. They were Telford and Wrekin, Shropshire County and Portsmouth City Teaching.

The government said average waiting times were low and stable at just 8.1 weeks for inpatients, similar to the same time last year, and that nine out of 10 inpatients started treatment within 18 weeks of referral. Simon Burns, the health minister responsible for the NHS, said: "Patients should be treated as quickly as possible, and we are introducing a strong performance measure for 2012/13 to ensure those who are waiting longer than 18 weeks are not forgotten."

The new data shows that 326,553 admitted and 941,520 non-admitted patients completed their referral to treatment pathway last November. Of those, 91% of hospital inpatients and 97% of outpatients began their treatment in less than 18 weeks.

"We are pleased to see that the NHS is making progress in reducing the number of patients who are waiting a long time to start treatment," Burns said. "In the last two months the number of people waiting more than a year has almost halved."