Research conducted by the regulator found that almost a quarter of walk-in centres had closed in recent years despite enjoying a high level of popularity with patients.
Walk-in centres are open seven days a week for extended hours, don’t require pre-booked appointments and provide one-off treatment for minor illnesses or injuries.
There are around 185 centres currently operating in England, down from the 238 that were established during the last decade.
Catherine Davies, Monitor’s executive director of co-operation and competition, said some commissioners felt they paid twice for treating patients at walk-in centres. This is because patients were already registered with a GP surgery that is paid to provide primary care under the current list-based remuneration mechanism.
‘We are now asking for views on whether the payment system should be reformed to fix this,' she said.
Davies added that, while it was up to local commissioners to decide whether to keep a walk-in centre open or not, ‘we need to make sure that the needs of patients are fully considered before decisions are taken’.
The research found that Mondays and Saturdays were the busiest times for most walk-in centres, while four out of five users said they received the treatment they needed and would visit a walk-in centre again. They were found to be particularly popular with young adults, women and vulnerable social groups.
The most common reasons for visiting a walk-in centre were flu-like symptoms, skin complaints, eye or ear infections, and sprains or strains.
Responding to the report, health minister Lord Howe said patients should be able to access good quality out-of-hours NHS services, without having to go to accident and emergency.
However, he said that walk-in centres were not a one-size-fits-all solution.
'Family GPs, community services and pharmacists all have a part to play and it's good that Monitor is looking at how walk-in centres fit in,' he added.
'We're working with NHS England to ensure services are tailored to the local needs of patients and we've agreed a £3.8bn integration fund to help join up health and care services.'