Patients are still struggling to get GP appointments, although the Government's drive to force surgeries to open for longer risks duplicating services and could prove costly, MPs have said.
There is also "no credible plan" to stem the fall in the number of GPs or to recruit more to meet demand, they said.
In a new report, the Public Accounts Committee (PAC) said many GP services were closed to patients at times during supposedly core hours of 8am to 6.30pm on weekdays.
Almost half (46%) of practices closed at some point during these core hours, including 18% that closed by 3pm on at least one afternoon a week.
In some areas, 42% of practices closed by 3pm. This forced more patients to turn to A&E, the report said.
While NHS England has promised to clampdown on practices that close during core hours, it collects no data on availability of appointments during these hours.
"Without this information, it cannot know whether practices are offering appointments during core hours to suit working people, such as between 8 and 9am and between 5.30 and 6.30pm," the report said.
"Yet it is pressing ahead with plans to extend access in the evenings and at weekends to meet the needs of this working population."
What patients can expect during core hours, such as being able to book an appointment or collect a prescription, has also not been set down, MPs added.
They said: "There is a risk that new extended hours arrangements could prove expensive and duplicate existing out-of-hours services.
"The cost of providing these new arrangements would be 50% higher than core hours if clinical commissioning groups were to simply provide the minimum requirements set out by NHS England."
The report also said there had been "no progress" in the last year on increasing the number of GPs, despite a Government target to recruit 5,000 more by 2020.
The number had actually fallen in the last year, from 34,592 full-time equivalent doctors in September 2015 to 34,495 in September 2016.
The report said more trainees needed to be recruited, while existing GPs should be encouraged to stay on.
"But Health Education England still lacks a credible plan for ensuring that there are enough GPs and that they are in the right areas," it added.
MPs said Health Education England had increased the number of trainee GPs, but still did not manage to meet its recruitment target last year.
NHS England and Health Education England were also pursuing plans to encourage GPs to stay but did not have a "credible plan for how to develop a cost-effective, sustainable workforce".
In March, the chief executive of NHS England, Simon Stevens, said all GP surgeries must offer bookable appointments outside the hours of 8am to 6pm within the next two years.
While he acknowledged general practice was under pressure, he said there was a need to increase access to primary care.
He also pledged to cut funding for practices that had half-day closing.
Dr Chaand Nagpaul, GP committee chairman for the British Medical Association (BMA), said: "The promised recruitment of 5,000 extra GPs remains a pipe dream that shows little sign of materialising in the next few years.
"Precious resources are being diverted to offer routine weekend appointments in some parts of the country when, at the same time, many GP services are struggling to provide effective, safe care to their patients during weekday opening hours and in urgent care settings in evenings and weekends."
Professor Helen Stokes-Lampard, chairwoman of the Royal College of GPs, said: "GPs and our teams are working flat out to deliver more patient consultations than ever before - recent research has shown that our workload has risen 16% over the last seven years.
"The fact that patients are finding it difficult to make an appointment is not because we are not working hard enough, it is because we don't have the resources and workforce necessary to deliver the care and services our patients need and deserve.
"It is also not the case that just because face-to-face surgeries might not be taking place, patient care isn't being delivered via telephone or online consultations, or by GPs making home visits - and when a practice is temporarily closed, adequate cover arrangements will be put in place.
"We agree with the report that forcing GPs to work 8am-8pm, seven days a week, regardless of patient demand makes little sense and is not cost-effective - and we reiterate our concerns that this will simply detract from the routine five-day service we are able to deliver for patients."
A Conservative spokesman said: "Our growing economy means more money for the NHS - and a 14% increase in primary care funding - so 17 million people can already see a GP at evenings and weekends.
"Theresa May has been clear that she wants to see extended opening hours across the country - none of which could happen with Jeremy Corbyn as Prime Minister, propped up by a coalition of chaos that can't invest in the NHS."