Student nurses who are not up to the job are being allowed to work in UK hospitals, according to a report.
Thousands of nurses join the NHS each year
The Nursing and Midwifery Council, which regulates nurses, says some students who should fail their course are in fact passing.
In a report, it says senior hospital nurses, who look after students, are sometimes too afraid to fail them.
The authors of the report urged nurses and course lecturers to root out those who are not up to the job.
The report, called Failing Students, says many weak students are "given the benefit of the doubt" and allowed to continue in the profession.
It says senior nurses or mentors are sometimes too ready to allow failing students' personal problems to influence their judgments.
It urges mentors to contact teaching staff as soon as possible if they have any concerns about students.
The report says course lecturers must also shoulder some of the blame for not ensuring students know all they should.
'Difficult to fail'
"The research shows that mentors find it difficult to fail students," said the report author Kathleen Duffy, who works at Glasgow Caledonian University.
"Preparing mentors for their role and responsibility in a fail scenario is vital and must be backed up with adequate support from both education and practice."
Janice Gosby, a professional adviser at the Nursing and Midwifery Council, said the report gave important insights into the reasons why students were not failed when they performed badly in hospitals.
"Mentors are accountable for their decisions on fitness for practice that enable entry to the nursing register.
"It is the quality of these decisions that protects the public from incompetent practitioners," she said.
Nurse mentor Andy McGovern told Nursing Standard magazine that some of his colleagues had passed students even though they were incompetent.
"Sometimes mentors just cannot face failing students because they are scared
of the reaction.
"This is especially so if it is at the end of a long, hard day."
Shirley Bach, chairwoman of the Royal College of Nursing's education forum, said: "It's vital that mentors must focus on providing good quality clinical assessment to protect patients.
"If students are well supervised and supported they are able to develop safe
patient care competencies.
"However this is compromised by the high number of students needed to meet
the NHS workforce targets which are placing greater pressures on mentors."
Ms Bach said she wanted a UK-wide framework for supporting mentors and student
to ensure high quality placements.
The Department of Health said it was up to the Nursing and Midwifery Council to maintain standards on nursing courses.
"It is not appropriate for the department to provide direction on the content of nurse training," said a spokeswoman.
"It is the role of the regulator, professional bodies and higher education institutions in
collaboration with the commissioners and funders of education and training.
"The Nursing and Midwifery Council sets the standard and outlines requirements for pre-registration nurse education."