The shortage of nurses in the National Health Service is endangering patients and leading to rising levels of frustration among existing staff, the leader of Britain's nurses warned yesterday.

Tackling nurse shortages must be the priority for the Government to ease the pressure on the wards and stem the exodus from the profession, Christine Hancock, general secretary of the Royal College of Nursing, said.

Speaking on the eve of the college's congress in Bournemouth, to be attended by 5,000 nurses this week, Ms Hancock said the health service was short of 15,000 nurses and plans to boost intensive care and convalescent beds would increase the demand for staff.

In a Mori poll of 1,200 nurses, conducted for the congress, nine out of 10 said staffing levels were the most critical factor affecting standards of care.

Ms Hancock said: "The strongest message from this survey is that the NHS can't deliver good-quality care because of staff shortages. It is sending a message to government that nurses support their policies and are desperately keen, but they desperately need to get the resources to the front line."

She said one nurse had told her she cried with exhaustion every night when she went home. The nurse had her resignation letter propped behind the clock and would look at it before pouring herself a gin.

Another nurse had written in a letter how the wife of a terminally ill man had asked her to see him because he was in pain. When she replied that she would do so in a minute, after she had attended to other patients, the wife screamed at her that she was not fit to be a nurse. The nurse wrote: "She was right - so I gave it up."