NHS chiefs set out plans to spend £500m on seven-day GP services and extended access schemes by 2020/21 as part of the GP Forward View published earlier this year.
But findings from research on an extended access scheme in Manchester shows that funding of £3.1m across 56 GP practices generated savings in hospital worth just £767,976.
The study, published in PLOS Medicine, compared GP and A&E attendances in 2014 at the 56 practices funded to extend their opening hours into evenings and weekends with 469 practices across the area that did not receive this funding.
Researchers found a 26% 'relative reduction in patient-initiated emergency department visits for minor problems', which equated to 11,000 hospital visits.
The increase in out-of-hours GP appointments was significantly greater than the reduction in A&E visits, the researchers found. Just over 33,000 additional out-of-hours GP visits were made, compared with a reduction of just under 11,000 visits patient-initiated to A&E.
The researchers said that the study could not measure the impact on health outcomes, either positive or negative, from the changes - and called for further research into cost-effectiveness and sustainability of the access scheme. A&E savings alone were unlikely to justify investment in extending GP access, the researchers warned.
Lead author of the research William Whittaker, a research fellow in health economics at the University of Manchester, said: 'There’s a need for evidence that seven-day primary care has benefits to patients as on the basis of emergency department savings alone, extending primary care is unlikely to be cost-effective.
'Our study suggests that extending opening hours in primary care may be a useful addition to policies aiming to reduce pressures on hospital services, potentially reducing patient-initiated use of the emergency department for minor problems - but at a significant cost.'
GP leaders have also warned that extending GP services across seven days and evenings is stretching an already overloaded workforce even thinner, and that existing out-of-hours services have lost staff to extended access pilots.
Responding to the study, a DH spokesman said: 'This study sets out a key reason why the government is committed to improving access to GP services as part of our plan for a seven-day NHS. By ensuring patients have access to consistent, safe and high-quality care through their GP at evenings and weekends, we can reduce pressure on urgent and emergency care and offer real choice for patients.'