One in four 'unaware of GP out-of-hours care'
One in four people has not heard of out-of-hours GP services, figures show.
The National Audit Office survey of 878 people in England also found one in five was unaware of the new 111 urgent phone service.
The poll was part of a wider review which found the numbers using out-of-hours services had fallen by a third in six years to 5.8 million in 2013-14.
The watchdog said the drop could be a result of people being unaware of the service or lacking confidence in it.
The report noted the drop in people using out-of-hours had occurred as visits to A&E had risen.
But it also said it could be related to the launch of the 111 service last year, which has started handling some of the out-of-hours calls.
The findings come after a turbulent few years for out-of-hours care. GPs were allowed to opt out of providing services in 2004 - and nine in 10 have done so leaving it to local health bodies to find alternative providers.
Over the years reports have emerged of patients struggling to access services or being unhappy with the care they have received.
In the most recent patient survey - released earlier this month - 17% reported they felt services were poor.
NAO head Amyas Morse said: "NHS England has much to do to help secure improvements throughout the system and to increase its oversight.
"It should also work to raise public awareness of how and when patients should contact out-of-hours GP services and needs to be prepared to take the lead in integrating these services effectively with other parts of the urgent care system."
In terms of cost, it estimates the amount spent on the service stood at £400m last year - £75m less once inflation is taken into account than eight years ago.
However, it said as 111 had taken on some of the workload it was hard to make cost comparisons.
Dr Cliff Mann, of the College of Emergency Medicine, said there needed to be a re-think over the way out-of-hours services were designed because attempts to encourage patients to use them had so far failed.
He said: "Rather than persuade patients to find their way to services, we need to provide a range of services where the lights are on 24/7.
"That is why we are strongly advocating that out-of-hours care should be co-located with A&E services. This isn't a marketing problem to solve but a real life patient care issue."
Patients Association chief executive Katherine Murphy added: "Unless this issue is addressed, we will continue to see more pressure on an already overstretched A&E system, as patients visit emergency departments."
But Health Minister Lord Howe said improvements were already being made.
He said 111 was helping direct patients to the right place, while GPs were now taking on more of a role in challenging out-of-hours care where their patients have concerns.