A new 24-hour health hotline is failing patients, according to an undercover television investigation.
Channel 4's Dispatches programme, NHS Undercover, found the non-emergency 111 system had staff shortages, long waits for callers and in some cases ambulances were being called out unnecessarily.
Two reporters posing as trainee call handlers secretly filmed at centres run by the private health care company, Harmoni, which has a third of the hotline contracts in England.
Dispatches said the footage shot at the branches in Dorking in Surrey and Bristol reveals "serious failings in the system".
The programme said its reporters found many patients were left waiting for longer than the 10-minute target for a callback from a clinician and some workers who weren't clinicians were filmed giving medical advice to the undercover journalists.
They also uncovered concerns about training, staff shortages and fears the system is leading to unnecessary callouts for ambulances, putting additional pressure on an already stretched A&E service, Dispatches said.
One Harmoni call centre manager was secretly filmed admitting: "We had a very bad service. Still realistically on the weekends we still are unsafe. We don't have the staff to deal with the calls that are coming in."
Peter Carter, the Chief Executive of the Royal College of Nursing, called for "immediate intervention" at "governmental level".
However, a spokesman for Harmoni told the programme: "We provide a clinically safe service. We expect all staff to only provide advice according to their role and their level of training and take a zero-tolerance approach to any breach. Our audits show no evidence of widespread poor practice. Our staffing levels are extremely robust with around one clinical advisor to every four health advisers."
The 111 phone number was rolled out in April, replacing NHS Direct as the number to call for urgent but non-emergency care. But the line suffered many teething problems, with patients complaining of calls going unanswered, poor advice given, and calls being diverted to the wrong part of the country.