Thousands of nurses are quitting the British National Health Service every year, the Royal College of Nursing said Monday.

Around 50,000 British-trained nurses have left or retired in the past year, with just over 20,000 recruits joining and another 12,000 coming in from abroad, a report by Royal College says.

Reasons for leaving included rigid working hours, dissatisfaction with changes to the pension scheme, heavy workloads, the feeling of being undervalued and violence by patients.

Despite successful efforts to boost recruitment, it would need to double further by 2014 just to maintain existing staff levels should the trend continue, the report states.

Dr. Beverly Malone, general secretary of the Royal College, said nurses "are coming in the front door" but "falling out the back."

"The government has not only got to pay attention to bringing them in but keeping them in," she said.

She called for more flexible working hours, better childcare and guaranteed pension arrangements.