NHS waiting lists are at their longest for six years and an important target has been missed for the first time since 2011, official figures indicate.

The data suggests that more than 10% of patients are waiting more than 18 weeks for treatment for the first time in three years, while the total number of patients on the list has risen to 2,885,253 – the highest February figure since 2008. The number of patients waiting more than 18 weeks has increased by almost half since May 2010 to more than 30,000 and those waiting more than a year for their treatment was also at its highest for a year at 544.

According to Labour the figures are a consequence of the government wasting money on unnecessary NHS reforms, which could have been better spent on improving care quality.

Andrew Gwynne, the shadow health minister, said this means the prime minister is personally "responsible for the problems" associated with increased waiting times.

"Under David Cameron, waiting lists for operations are at their longest in years. He wasted £3bn on a damaging reorganisation and patients are paying the price. Labour left NHS waiting times at a record low but on David Cameron's watch the NHS is heading back to the bad old days with patients waiting months on end for treatment in pain and discomfort. This is further proof that Tories cannot be trusted with the NHS."

Dr Barbara Hakin, chief operating officer of NHS England, acknowledged that the NHS faces a "challenge on the 18-week standard" but added that staff are "working incredibly hard to ensure patients are seen quickly".

"During February, around 270,000 patients were admitted for treatment within the standard, and around 400 waited longer than we would have liked," she said. "This shows we are treating more patients than ever, but we do need to treat patients in order of clinical priority. This means treating those who have waited the longest, which may mean that we miss the standard.

"We are determined to redouble our efforts so that we do meet the standard and 90% of patients are treated within 18 weeks. But this may take several months as it is imperative we focus on those who have waited longest."