But GP leaders highlighted previous research that contradicted the latest findings, and warned that successes in pilot areas were only achieved through 'significant, additional short-term funding'.
They also warned that soaring pressure on existing services meant that many practices were 'barely able' to provide adequate services over five days a week.
Across the full seven-day week, A&E vists from patients at pilot practices were down 10%, according to the University of Sussex researchers. Visits to A&E were down 18% on Saturdays and Sundays.
Seven-day GP services
The findings, published in the Journal of Health Economics, also showed a reduction in A&E admissions and ambulance call-outs in the pilot areas.
The researchers wrote: 'We find most of the reduction comes from a drop in cases of moderate severity (usually patients treated and discharged with instructions for follow-up with GPs or specialists).
'One would expect little or no effect on the most serious cases. Indeed, we find no impact on the count of A&E attendances that are induced by accidents. However, we do find an impact on A&E admissions which are also likely to be serious cases. This effect is entirely driven by an 19.2% fall in weekend A&E admissions of patients aged 60 years and above.
'Our intuition for this result is that A&E medical staff could be particularly risk averse when dealing with an elderly patient since at the time of consultation, they typically lack access to the patient’s medical history. If in doubt, A&E physicians are likely to err on the side of caution and opt to admit such a patient. In contrast, had the same patient visited their GP, they might have been treated and sent home instead.'
Researcher Dr VIkram Pathania said that despite early evidence from Challenge Fund pilots that weekend opening was underused by patients, there was 'clearly unmet demand for weekend GP opening'.
He added: 'Seven-day opening for GPs appears to make a dent in two major sources of A&E expense – admissions and ambulance usage.
'Costs aside, there is also strong evidence that patient healthcare, in many cases, could be better delivered by a visit to a GP. Typically A&E doctors are junior to GPs, who are equivalent to hospital consultants in terms of their medical training and expertise. Plus GP treatment is based on direct past experience with the patient and access to their medical records.'
However, the researchers warned that extended GP weekend access could simply create additional demand, and highlighted that more work in primary care would require a transfer of funding from other NHS services.
GPC deputy chairman Dr Richard Vautrey said: 'GP practices are currently under incredible strain from rising patient demand, falling funding and chronic staff shortages that have left many barely able to provide enough appointments to the public during the working week.
'This study needs to be taken alongside others which haven't shown a significant reduction in hospital activity and it should also be noted that schemes such as this have only been possible through significant additional, short-term funding.
'Many of the pilots have shown that appointments provided on a Sunday were not used by patients, wasting vital NHS resources. Current GP services badly need significant new funding to enable an immediate increase in staff to allow GPs to be able to meet the growing needs of their patients. This should be a priority before there can be any expansion in what practices already offer.'