The NHS is still short of nurses and the situation could get worse, the UK's biggest nursing union has warned.
An estimated one in five NHS nursing posts are vacant
The Royal College of Nursing (RCN) says government efforts to recruit extra nurses are not delivering the numbers needed to fill vacant posts.
It warns that plans to create foundation trusts in England could make things even worse.
But the Department of Health says progress is being made and that more nurses than ever before are now working in the NHS.
A report, published by the RCN on Friday, shows that the equivalent of 32,000 full-time nurses have joined the NHS since 1999.
However, these extra nurses are not spread evenly across the UK.
While England has seen an 11% increase in nurses, growth in the rest of the UK is significantly lower.
In Wales, there are now 8% more nurses than there were four years ago. In Northern Ireland, the figure is 6% while in Scotland there has been only a 5% increase.
The RCN warns these variations could get worse if the proposed foundation hospitals in England are allowed to offer better terms and conditions to nurses and other staff.
It said this could lead to some nurses leaving hospitals in Scotland, Wales and Northern Ireland in favour of better paid jobs in England.
The report also indicates there are still serious shortages in some specialities.
While some specialities have seen double-figure growth, the number of midwives and nurses working in learning disabilities, for example, has fallen.
In addition, the report suggests the NHS is heavily dependent on nurses from overseas to fill vacant posts.
Almost half of all of the extra nurses who have been approved to work in the UK over the past four years are from overseas.
There is a concern that these nurses are more likely to leave the UK if they get a better offer elsewhere.
The report indicates a large number of nurses are still leaving the profession, with almost 20,000 leaving last year.
That figure is expected to rise in the coming years - not least because a greater proportion of nurses are now approaching retirement age.
The report also suggests government efforts to encourage nurses who have left the NHS to return to work are failing.
The number of nurses returning to work in the NHS has remained at about 3,700 each year for the past few years.
The RCN is urging health ministers throughout the UK to work together to try to tackle the shortage of nurses and to ensure the extra nurses are spread evenly.
Beverly Malone, RCN general secretary, said failure to address the problem could damage patient care.
"The severe imbalance in the rate of growth of the UK nursing labour workforce is putting the future of patient care at risk.
"It requires an urgent co-ordinated action plan by the UK's four health departments."
A spokeswoman for the Department of Health said its recruitment policies were working.
"There are more nurses than ever before working in the NHS," she said.
"Over 15,000 nurses have returned to the NHS since 1999 and there has been a 55% increase in the number of nurses in training in the last six years.
"Our staff are the backbone of the NHS and the contribution of internationally recruited staff to the NHS is invaluable.
"But international recruitment is just one initiative to build the NHS workforce which includes offering more flexible working patterns, better pay and childcare provision.
However, shadow health secretary Liam Fox said the RCN report revealed "a number of shocking trends".
"The government's promise to attract back nurses who have left the NHS was worthless - figures have been low and static for some time and huge numbers of nurses are simply leaving the register. "
Liberal Democrat health spokesman Evan Harris said: "These figures demonstrate a demographic time bomb, where within five years a quarter of our nurses will be eligible to retire. Time is running out for ministers."