Latest performance data reveal number of English patients waiting more than 18 weeks has risen by 26% in last year

Doctors are blaming financial pressures on the NHS for an increase in the number of patients who are not being treated within the 18 weeks that the government recommends.

New NHS performance data reveal that the number of people in England who are being forced to wait more than 18 weeks has risen by 26% in the last year, while the number who had to wait longer than six months has shot up by 43%.

In March this year, 34,639 people, or 11% of the total, waited more than that time to receive inpatient treatment, compared with 27,534, or 8.3%, in March 2010 – an increase of 26% – Department of Health statistics show.

Similarly, in March this year some 11,243 patients who underwent treatment had waited for more than six months, compared with 7,841 in the same month in 2010 – a 43% rise.

Despite rising demand for healthcare caused by the increasingly elderly population and growing numbers of people with long-term conditions, the NHS treated 16,201 fewer people as inpatients in March 2011 compared to March 2010, the latest Referral To Treatment data disclose.

The British Medical Association said the longer waits and fewer treatments were inevitable: "Given the massive financial pressures on the NHS, it was always likely that hospital activity would decrease and waiting times would increase," said a spokesperson.

"The capacity of hospitals has been limited by staffing freezes, and commissioners of care are under pressure to ration surgical procedures considered to be of low value. As well as the personal impact on individual patients, there is a potential long-term consequence for NHS hospitals, which are at risk of being financially destabilised as they lose income."

Labour claimed the figures proved that the NHS was declining as a result of the coalition's health policies. "Another month, another breach of the treatment waiting times target. This is further evidence of the NHS going backwards again under the Tories," said John Healey, the shadow health secretary. "Instead of ploughing on with a wasteful top-down reorganisation of the NHS, David Cameron and Andrew Lansley should now apologise to those patients having to wait longer for treatment."

Katherine Murphy, the director of the Patients Association, said it had heard from people whose hip or knee replacement had been postponed once or twice without them being offered a new date, leaving them in pain and with their independence compromised.

The DH said: "Waiting times go up and they go down, but this data shows that waiting times remain broadly stable. On average, admitted patients waited 7.9 weeks for treatment in March 2011, compared to eight weeks in March 2010. For outpatients it is just 3.7 weeks, compared to 3.8 weeks in 2010."