Image copyright NHS Image caption General call handlers at the non-emergency 111 are not medically trained

The NHS has started an investigation after pictures emerged showing "exhausted" medics at a 111 call centre seemingly asleep on duty.

A former senior call adviser for the non-emergency hotline claimed in a Daily Mail article staff at the Dorset site were "overworked".

The centre has recently been criticised after the death of a baby in Cornwall.

South Western Ambulance Service, which runs the service, said it "strongly refuted" allegations in the article.

Doubts have been raised about the 111 service, where non-medically trained call handlers work alongside a limited number of clinicians, after the death of baby William Mead in 2014.

Image copyright William Mead's family Image caption William Mead died aged 12 months in December 2014 after suffering from a persistent cough

A report on his death said he might have lived if call handlers realised the seriousness of his condition.

Whistleblower Sarah Hayes, who is a former member of staff, told The Daily Mail there was "frequently" no on-call clinician at the trust's call centres in Dorset or Devon.

She told the newspaper: "The nurses and paramedics we did have were so exhausted and overworked that some would fall asleep on shift.

"I was angry, of course, but I don't feel it was their fault. Put simply, they were exhausted.

"I think anyone with experience of 111 would say it has problems for young babies, and it's really hard to get a good assessment done."

She said she repeatedly raised her concerns with management but was branded a "troublemaker".

Ken Wenman, chief executive of South Western Ambulance Service, said the organisation had worked to "put the necessary measures in place to prevent something similar from happening again".

He said: "There are a number of allegations made in the Daily Mail that we strongly refute, however, there are actions that Sarah Hayes says she took, for which we can find no paper trail or audit, and therefore an investigation into these allegations has been commissioned.

Joyce Guest, chair of Healthwatch Dorset, described the claims as "very disturbing".

She added: "The service needs to be adequately staffed at all times. Exhausted staff are more likely to make mistakes. And there needs to be enough medically trained staff available at all times, in addition to call handlers."

A spokesperson for NHS regulator Monitor said it would work closely with the trust while it looks into the "issues".