Its annual survey of hospitals across the UK suggests there are 25,000 vacancies at the moment.

And it warns that the situation could get worse rather than better, with one in nine nurses planning to quit over the next two years.

The Department of Health says progress is being made and 55,000 nurses had been recruited since 1997.

Official figures

The RCN report says nurses who work on a rotating pattern of day and night shifts are most likely to want to leave.

This rotation system is used widely in NHS hospitals. However, Beverly Malone, general secretary of the RCN, said many nurses disliked it.

"It's clear from our survey that it is unpopular with many nurses.

"For some, it can be even damaging to not only their physical and mental wellbeing but also their relationships with families and friends.

"Everyone has a right to make choices about the balance they want between work and life.

"Forcing nurses to work an internal rotation shift pattern denies them this basic right."

Vacancies

A report from the department, published last July, claimed there were just 8,000 vacant posts.

However, officials only count posts that have been vacant for more then three months.

The RCN says this means that thousands of vacancies are not being counted.

It estimates that there are 19,000 vacant jobs. However, since many nurses chose to work part-time it says 25,000 extra staff are needed.

'Good progress'

The government's chief nursing officer Sarah Mullally said progress was being made.

"There are 55,000 more nurses in the NHS than in 1997," she said.

"However, the department is not complacent and knows there is always more work to do."

Ms Mullally said the government "is working hard" to introduce flexible working for nurses

She welcomed other parts of the RCN survey which suggested 78% of nurses are enthusiastic about their jobs and 75% think nursing is a rewarding career.

But Shadow Health Minister, John Baron, said: "Against all advice, ministers continue to micromanage the NHS from Whitehall.

"As a result, nurses spend their time tied up in red tape monitoring whether centrally set, and often unethical, targets are met."

Liberal Democrat health spokesman Paul Burstow added: "The government must sit up and take notice of this worrying research."