There has been a "worrying" fall in the number of nurses working in the NHS, new analysis from an influential think tank has found.
The King's Fund said there were fewer nurses working in the NHS in England in April this year compared with the previous April, the first year-on-year monthly fall since April 2013.
In April 2016 there were 285,080 "full-time equivalent" nurses and health visitors employed by the NHS in England but in April this year there were 284,619.
The trend continued in May and June, the health charity found.
In June 2016 there were 283,674 full-time equivalent nurses and health visitors employed by the NHS in England but in June this year there were 282,603 - a reduction of 1,071.
The King's Fund raised concern about the figures, adding that having enough nurses was "essential" for delivering safe care for patients.
It stressed that it was important to monitor year-on-year figures as there were annual seasonal fluctuations in the workforce.
There could be several factors at play, including a 96% reduction in the number of European nurses joining the UK register following the EU referendum and changes to language tests, the think tank said.
The King's Fund said another issue was staff leaving as a result of ill-health and work-life balance, which had "risen sharply since 2010".
While the think tank welcomed a Government announcement to increase nurse training places, it warned that it would take years for this to translate to more nurses on wards.
Last week Health Secretary Jeremy Hunt announced a 25% increase in nurse training places to boost numbers of home-grown NHS staff as Britain leaves the EU.
The additional 5,000 places will bring the number of undergraduate study opportunities to 25,850 in 2018/19.
But the King's Fund said that initial indications suggested that the Government's decision to scrap bursaries for student nurses had resulted in a reduction in successful applicants.
Richard Murray, director of policy at The King's Fund, said: "There is good evidence that having enough nurses is essential for delivering safe care, and so it is worrying that the number of nurses is going down at a time when services are already overstretched and the demand for care is rising.
"While last week's announcement of an increase in nursing training places is welcome, it will take years for this to translate into extra nurses on the wards.
"Workforce planning has been neglected for too long in the NHS, and the fact that the EU referendum result appears to have tipped the balance highlights how fragile the workforce situation has become.
"A new workforce strategy is desperately needed."
Responding to the figures, a Department of Health spokeswoman said: "This analysis refers to overall numbers for nurses and health visitors.
"Patients should be told that we actually have more nurses on our hospital wards since April 2016 not fewer, which alongside last week's announcement of the biggest ever increase in nurse training places underlines our commitment to ensuring the NHS has the nurses it needs to provide the best possible care for patients, both now and in the future.
"There are also 3,193 more EU nationals working in the NHS than at the time of the referendum.
"We have been absolutely clear that they play a vital role in the NHS and want to see their excellent work continue long after the UK leaves the EU."
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