An out-of-hours GP service covering 250,000 patients is using senior nurses when doctors cannot be recruited to work the shifts, it is reported.
The firm, Harmoni, regularly employs advanced nurses to work eight-hour overnight shifts covering districts of up to 150 square miles, a whistleblower claims.
In times of extreme staffing shortages, there has been just one advanced nurse practitioner working overnight in North Somerset, the Daily Mail said.
The whistleblower told the newspaper that locum doctors have been flying in on easyJet from Europe, or driving from elsewhere in Britain to perform back-to-back shifts round-the-clock; terminally-ill cancer patients have waited eight hours for a doctor to visit them at home and administer pain relief; and foreign doctors with a poor grasp of English have been used to plug gaps in the rota.
The whistleblower said that working for Harmoni was like "taking a loaded gun and sitting with it because at some point it's going to become so unsafe it's going to go off".
"My personal feeling is that at times it has been unsafe," the source said. "It's a dereliction of duty. Everything is secondary to meeting budget. Patient care is compromised, employee care compromised. It's an edict from on high. They have thinned rotas down to a bare minimum."
A spokesman for Harmoni said: "The clinical staff employed by Harmoni are all self-employed GPs or advanced nurse practitioners who work on flexible contracts. Harmoni has comprehensive measures in place to ensure team members take sufficient breaks. Harmoni has in place some of the most robust interviewing procedures in this field to ensure the communications skills of GPs who work for us are of a high standard.
"On very rare occasions, and only after consultation and agreement with our commissioning colleagues in North Somerset that the service remained clinically safe, we have run an overnight shift with a very experienced advanced nurse practitioner providing the first point of contact with a GP available on-call to support with any advice needed GPs available to support if a home visit was necessary.
"For Harmoni, and indeed virtually all out-of-hours providers, there are some occasions where filling all the planned GP rota slots is a challenge. Even when this is the case we ensure we are providing a service which is clinically safe and our service is constantly closely monitored by NHS commissioners to ensure this is the case. Our performance figures are accurately recorded in line with national guidelines and, again, carefully scrutinised by our commissioning colleagues."
A Department of Health spokesman said: "It is a legal requirement for the NHS to make sure the right, high quality out-of-hours services are in place for patients in their area. If this is not happening it is totally unacceptable and we expect the local NHS to take action immediately to improve their services."