Closing walk-in centres may make it harder for people to see GPs – and risks sending more people to A&E, warns healthcare regulator Monitor.
It reviewed the walk-in centre service after the closure of 50 of the 230 in England in the last three years.
Monitor found the centres are popular with the public, but critics fear they can mean duplication of services.
The government said walk-in centres were “one part” of out-of-hours care.
As part of its review, Monitor surveyed just under 1,900 patients at 20 walk-in centres.
When patients were asked where they would have gone if the walk-in centre had not been available, 21% said they would have gone to A&E, while a third would go to their own or a different GP.
The poll also found 22% had tried to contact a GP practice but found no appointment, or none at a convenient time.
And 24% did not even try to contact a GP because they did not think they would get an appointment.
Former Prime Minister Tony Blair announced plans to establish the first walk-in centres in 1999.
They provide routine and urgent primary care with no need to pre-book or be registered. Most are GP-led, though some are overseen by nurses.
Private companies, such as Virgin and Care UK, currently run around a sixth of the centres.
The Monitor review found that walk-in centres were more likely to be used by those aged 16-45, with women slightly more likely to attend.
Those that have closed have done so due to concerns they are not helping A&E.
Many contracts for walk-in centres are up for renewal in 2014 and the review found confusion about who should decide on their fate, and said decisions had possibly been put off because of the upheaval in the NHS.
Some commissioners also felt they were “paying twice” for patients, once with the GP they are registered with and a second time for their treatment at the walk-in centre.
But Monitor said there should be careful thought about possible closures.
Catherine Davies, Monitor’s executive director of co-operation and competition, said: “We’ve been told that one in five people would choose to go to an accident and emergency department if the walk-in centre wasn’t there for them.
“While it is for commissioners to decide whether to keep a walk-in centre open, we need to make sure that the needs of patients are fully considered before decisions are taken.”
The review suggests the payment system to be changed so GPs have more of an incentive to be flexible, providing online or phone consultations, improving receptionist skills, extending hours or offering walk-in appointments.
Dr Chaand Nagpaul, chair of the British Medical Association’s GPs committee, said the association supported walk-in centres where there was a “clear need”.
But he said a government requirement for a centre in each – now abolished – primary care trust area meant they were often opened in places with little patient demand.
The London Victoria centre closed in 2011
Dr Nagpaul added: “The result has been a lot of money being spent on these facilities with some now closing because commissioners have found there is not sufficient demand, or that they are not value for money.”
He said that at a time of severe financial pressure on the NHS, commissioners had a duty to ensure funding was properly allocated and avoid a duplication of services.
Peter Carter, general secretary of the Royal College of Nursing, said: “This winter, demands on the health service mean that primary care and the hospital sector need to work together seamlessly and efficiently to stop the service as a whole from buckling.
“Walk-in centres can have a crucial role in plugging this gap.”
Health minister Lord Howe said: “Patients should be able to access good quality out-of-hours NHS services, without having to go to an A&E.
“Walk-in centres may be part of the answer but this isn’t a one-size-fits-all solution.”
But Andy Burnham, the shadow health secretary, said: “People need services and support seven days a week and that is why the last government introduced NHS Direct and walk-in centres.
“The decision to dismantle them is one of this government’s worst acts of vandalism and patients are paying the price.”