Jeremy Hunt has ordered an investigation into NHS 111's response to a "very ill" three-week-old baby who was left untreated overnight and later diagnosed with meningitis.
The Health Secretary defended the non-emergency helpline as an improvement on the previous advice service, although he conceded it is "clearly not perfect" as he pledged to investigate the incident.
Mr Hunt was informed of the case by Labour MP Teresa Pearce, who is the grandmother of the baby girl involved.
Ms Pearce said the girl's parents had been promised a visit from the duty doctor by the 111 call-handler but he did not arrive.
The Erith and Thamesmead MP told Mr Hunt: "A recent whistleblower revealed that the 111 helpline is in meltdown and at least two babies have died after staff failed to recommend treatment that may have saved them.
"Two weeks ago my own three-week-old premature granddaughter was very ill. Her parents called 111 and were promised that the duty doctor would call. He did not.
"They waited the whole long night and the next morning took her to A&E and she was diagnosed with meningitis.
"What exactly are you doing to fix the crisis in the 111 service?"
Mr Hunt replied: "This is a very serious issue and I will happily look into it personally to make sure that a full investigation is happening into the incident you talk about, which clearly should not have happened.
"The 111 service has, I think, been an improvement on what we had before - it's taking nearly three times as many calls as the previous service that it replaced - and around a quarter of those are referred to a clinician.
"But it's clearly not perfect given the stories you have said, so I will look into the case you have raised."