Growing numbers of critically ill patients are coming to harm as a result of inadequate care provided by NHS staff, new figures reveal.

The number of “serious incidents” involving what the NHS calls “sub-optimal care of deteriorating patients” is going up in hospitals, ambulance services and mental health settings.

The trend has emerged in previously unpublished NHS England figures provided to former Liberal Democrat health minister Norman Lamb, who has branded them “deeply disturbing”.

They also show that the number of patients in hospital in England who are suffering harm in serious incidents because of delays in their treatment has risen significantly over the last two years from 700 for some of 2015-16 (only part-year figures were available) to 1,027 in 2016-17, and then again to 1,515 last year.

The number of serious incidents of all kinds that occurred in acute hospitals fell slightly between 2015-16 and 2017-18, from 12,303 to 11,637 – a 5% fall. However, rises in several types of incidents needed to be investigated by NHS England because they involve potentially serious damage to someone’s health, said Lamb.

“The figures show there have been disturbing deteriorations in performance in some vital areas of patient safety,” Lamb told the Observer. He said that increases should be a cause for concern for NHS England, given the NHS’s five-year “patient safety crusade” since the report into the Mid Staffordshire NHS care scandal in 2013.

And the ex-coalition health minister added that it is “inevitable” that understaffing across the NHS is likely to be “a key factor” in the increases, with doctors and nurses unable to give every patient the time and attention they need because of the growing demand for care.

NHS Improvement, the health service regulator, said the NHS was short of 93,000 staff during 2017-18, including 37,000 nurses and 10,000 doctors.

The number of recorded serious incidents involving sub-optimal care of deteriorating patients in hospital rose 10% from 580 in 2015-16 to 636 in 2017-18, NHS England’s data showed.

Among England’s 10 regional ambulance trusts, it rose 28% to 119 from 93 a year earlier, and in England’s 54 mental health trusts it went up 16% from 91 in 2016-17 to 106 last year.

Similarly, serious incidents involving treatment delays rose from 1,027 in 2016-17 to 1,515 last year, while among ambulance trusts they increased from 228 to 385 over the last two years.

The figures do not indicate what harm, if any, patients suffered as a result of the lapses in patient safety. However, incidents include cases involving severe harm or even death.

Hospitals have also seen increases in the number of such incidents involving surgery or other invasive procedures (up 16% over the last two years to 865) and diagnostic incidents, which includes delays and failure to act on test results – up 28% to 1,195.

However, leaks of confidential information and the number of patients suffering a slip, trip or fall while in hospitals have both fallen. Serious incidents in mental health settings have fallen 11% over the last two years from 5,152 to 4,611.

Incidents involving self-harm and abuse of adult patients are down but those involving an apparent, actual or suspected homicide have risen to 76 a year.

A spokesperson for NHS Improvement said patient safety was a top priority for the NHS: “When serious incidents occur we expect NHS providers to investigate and get to the underlying causes of what happened. The purpose of these patient safety investigations is to establish learning so local, and in some cases national, changes can be made to ensure patients are kept safe and staff are supported to prevent similar incidents occurring.”