Pilot schemes set up by the Prime Minister to improve seven-day access to GPs have cut their hours, partly due to a lack of demand, according to an investigation.
Of 18 pilot schemes, eight have now either cut weekend or evening hours, or stopped providing the service altogether, research by the GP magazine Pulse found.
In October 2013, David Cameron announced a £50 million Challenge Fund to help improve access to general practice.
The first wave of 20 pilots was announced in April 2014.
Further funding of £100m for 2015/16 was announced by the Prime Minister in September last year. In March, 37 more pilot sites were announced - the second wave.
Ideas being tested by the pilots include extended opening hours, more ways for patients to access services and new services to support patients with complex needs.
The Pulse investigation looked at 18 pilot sites in the first wave who were offering weekend appointments to patients.
In Devon, the Devon Doctors Group running part of the pilot in south-west England told Pulse that its four 9am to 5pm Saturday and Sunday appointment sites were "no longer in operation".
NHS Slough Clinical Commissioning Group (CCG) said its pilot has reduced weekend access to four hours on Saturday and Sunday, having originally offered 9am to 5pm on both days.
In Derbyshire, there are still two seven-day hubs, but they have cut hours from four hours a day to two hours on weekdays, and 12 hours a day to three hours at weekends.
Five CCGs in north-west London have cut hours for their seven-day access pilot. The North West London Collaboration of CCGs said they have "focused on supporting practices to work together as federations".
Other pilots have proved unpopular with patients, Pulse said.
A spokesman from Londonwide Local Medical Committees (LMC), which represents London GPs, told Pulse: "The CCGs have found that weekend opening is not as popular as first thought, so weekend hours covered have been modified."
Dr John Ashcroft, executive officer at Derbyshire LMC, said his local pilots have taken money away from existing services.
He said: "It may tick the seven-day access box for managers and the Department of Health, but has made little difference to patients - except confusing them with initiatives that are not joined up."
Pulse editor Nigel Praities said: "This surely must be a wake-up call for the Prime Minister. His plan to roll out seven-day access to GPs is floundering, and he must look at diverting the funds to shore-up core services instead."
A spokesman for NHS England said: "A national evaluation of the programme will be published with more information on each of the pilots."
Dr Peter Thomas, medical director of the Bury GP Federation, which runs a wave one pilot, said: "We set out to make GP appointments more accessible for patients, particularly parents, carers and people who work, fitting in around their busy lives.
"We are very proud of the pace and scale of what we have achieved and that we are now offering truly flexible options for people in Bury who otherwise would have struggled to see a doctor."
A spokeswoman for the Department of Health said Pulse had an "agenda" regarding seven-day working but patients wanted to see GPs in the evenings and at weekends.
She added: "This anecdotal investigation does not contain the full facts.
"Earlier this year some pilots told us they extended their opening hours further following patient demand and an independent first evaluation of the wave one schemes will be published soon."