A privately run NHS walk-in centre has launched a probe after safety complaints by a former doctor.
Four privately run commuter walk-in centres are open
Dr Anila Reddy, who has resigned from his post as lead GP at the centre in Canary Wharf, London, raised his concerns in a letter to the government.
He said nurses were being encouraged to work beyond their remits to drive down waiting lists, Doctor magazine said.
The government said Atos Origin, the firm which runs the centre, had launched an investigation.
The Canary Wharf service was one of four privately run centres set up close to rail and other transport stations to provide care for minor illnesses.
The centres were designed to allow people who do not work close to their GP practices to access primary care services more easily.
The services are run by nurses with a GP constantly on site to offer expert advice.
Over 22,000 patients have been treated by the four centres, with another three in the pipeline.
Dr Reddy, who had been the lead GP at the centre since it opened in April, told Doctor he was concerned about how the services was run. He resigned earlier this month.
"Nurses who are of variable experience and training are being allowed to see patients without the usual compulsory protocols, which are absolutely necessary for patient safety, and are being encouraged to see as many types of patients as they can to ensure waiting time targets are attained."
He wrote to the Department of Health setting out his concerns, which has now asked Atos Origin to investigate.
A spokeswoman for Atos Origin said: "Patient safety is of the utmost importance and any claim regarding patient care and safety is taken extremely seriously.
"As a result of these claims, we have now started an investigation into these alleged incidents."
A Department of Health spokesman added: "We have not seen any evidence to support these accusations nor is there any reason to question other independently-run NHS walk-in centres.
"In fact, walk-in centres run by independent providers are subject to more scrutiny than those run by the NHS as all NHS walk-in centres run by independent sector providers are subject to strict regulation by the Healthcare Commission."