According to analysis by the Nuffield Trust think tank for the BBC, more than 40,000 nurses have quit the NHS in the past year. This amounts to one in nine of the workforce.

The research shows that many of those leaving are skilled and knowledgeable nurses, who could still work for many years.

A spokesperson for the Department of Health and Social Care said the government was halfway to the target of increasing the number of NHS nurses in England by 50,000 during this parliament.

However, one in 10 nursing positions are currently vacant.

According to the spokesperson, a workforce strategy will be published soon, which sets out how the NHS will recruit and retain nurses.

However, the Nuffield Trust warned that the government will struggle to hit this target, unless something is done to stop nurses leaving.

According to the research, stress and work-life balance are key factors in nurses' decisions to leave the NHS.

Dr Billy Palmer, from the think tank, said that it was very concerning that factors besides retirement are becoming a major reason for nurses leaving the NHS and that this suggests that there are deep-rooted issues with working practices and employment conditions.

He said: "Nurses are integral to the functioning of the health service - it should be an urgent wake-up call."

The research found that the proportion of nurses quitting in Scotland was the same as in England. Although similar data is not available in Wales and Northern Ireland, other indicators suggest that significant numbers of nurses are leaving.

NHS managers are also warning that the situation will get worse as the cost-of-living crisis continues. An NHS Providers report concluded that the squeeze on pay is forcing nurses and other NHS staff out of the NHS or into making decisions such as stopping pension contributions, skipping meals and taking on second jobs.

Miriam Deakin, from NHS Providers, said: "The sad fact is some can earn more working for online retailers or in supermarkets."

She also warned that the staff shortage will have an impact the NHS's ability to tackle the backlog.

She added the NHS was reaching a "tipping point" when it comes to the workforce, and the shortage of staff threatened to hamper the ability of the health service to tackle backlogs in treatment.

The data for the research came from NHS Digital and includes those in permanent roles at NHS trusts that provide hospital, community and mental health care. Those working in general practice are not included.

The data shows that nurses in the community were most likely to leave their job.

From the NHS Digital data, it is not possible to tell why people are leaving, so to establish this, the Nuffield Trust used other sources including research by the Nursing and Midwifery Council.

Research by the regulator earlier this year, found that after retirement, personal circumstance, too much pressure, workplace culture and leaving the UK were the most common reasons for leaving the health service.