Thousands of patients left waiting months for treatment at Dorset County Hospital were still in limbo at the end of October, the latest figures reveal.

The Patients Association says long waits can be unbelievably stressful, and blames a "familiar cocktail" of underfunding, poor planning and higher demand for increased waiting times.

According to NHS rules, anyone referred by their doctor for non-urgent consultant-led care should start treatment within 18 weeks.

But NHS England statistics show that 4,897 patients due to be treated at Dorset County Hospital NHS Trust had been waiting longer than that at the end of October – 30 per cent of those on the waiting list.

It means the trust is falling well short of the NHS’s target for the 18-week threshold to be met in at least 92 per cent of cases.

Of those not seen in time, 710 had waited more than 36 weeks, while five had still not started treatment after a year.

The figures quoted only cover those still waiting to start treatment, and do not account for how long patients who started treatment waited.

Across England, 85 per cent of patients waiting to start treatment at the end of October had been doing so for 18 weeks or fewer – below the target.

This was the lowest proportion for the month since 2007.

Lucy Watson, chairman of the Patients Association, said that longer waits for patients were "unacceptable".

She added: "The rising trend in waiting times is very clearly attributable to the familiar cocktail of sustained NHS underfunding, poor planning and stewarding of the NHS workforce, and rising levels of patient need linked to demographic change.

"The Government will have to go well beyond its current spending plans in order to reverse this trend decisively.”

Professor Andrew Goddard, president of the Royal College of Physicians, said that while targets can drive improvement, they would be hard to achieve without a "much-needed injection" of staff.

“Our data shows that 43 per cent of consultant posts went unfilled last year, partly due to the fact that there simply aren’t enough people training to become doctors," he added.

“We need the Government to commit to doubling the number of medical school places, so that we can truly create a workforce that is fit for the future.”

A spokesman for Dorset County Hospital said: “We recognise that waiting for a procedure can cause anxiety and frustration for patients and their families, and we are doing everything we can to minimise waiting times, working closely with our local healthcare partners.

“Like hospitals throughout the country we have experienced significant increases in referrals and emergency admissions so our services are under a lot of pressure. Our staff are working extremely hard to see patients as quickly as possible and our priority remains providing safe, high quality care.”

The NHS is reviewing the waiting time target, which it says can lead to problems such as a lack of focus on how long some patients wait beyond 18 weeks.

It is considering an average waiting time as a possible alternative.

A Department of Health and Social Care spokesman said there are 19,300 more doctors on wards than in 2010.

She added that the Government is funding an extra 1,500 university places for future doctors alongside "ambitious" plans to increase the NHS workforce, backed by increased funding worth £33.9 billion extra a year by 2023-24.