More than five million people across England are unable to book an appointment with a GP outside of working hours.
BBC analysis of official data shows 10% of registered patients live in areas where there is no access to GPs on evenings and at weekends.
Labour has accused the government of "breaking its promises".
NHS England said it was still on target to provide access to extended care for all patients by 1 October.
Our analysis shows:
- More than 22 million people - or 40% of patients registered with GPs - now have "seven-day 8am to 8pm" access to GPs - defined as full provision by NHS England
- Just over half the population have access to partial provision. This is when a GP practice can offer the minimum of ninety minutes of bookable appointments once a week
- Only two areas offer full provision to GPs for all patients
- Some 5.4 million people - or 10% of patients - had no access to GPs outside of normal working hours
What are extended hours?
Former Prime Minister David Cameron made a promise everyone in England would have access to GP services seven-days a week by 2020, at the Conservative party conference in 2014..
The plans have since been brought forward. From October, it will be mandatory for all Clinical Commissioning Groups to put in place arrangements for extended access to general practice.
The latest data - from March and collated bi-annually from surveys filled out by GPs - shows widespread regional variation.
In Sefton in Merseyside, for example, two thirds of patients had no access to GPs outside of working hours, the highest percentage in England.
That compares to Herefordshire and Rushcliffe in Nottinghamshire, where every patient had access to full provision.
A spokesman for NHS South Sefton CCG said extended access to general practice was "not compulsory", but it was "undertaking a procurement exercise" to roll services out from October.
'An appointment ten days ahead'
Self-employed, mother of three, Pragya Agarwal is registered at a GP practice commissioned by NHS Southport and Formby CCG.
No practices provide a full 8am-8pm service, but 94% of patients have access to some form of partial provision.
Pragya said it was often impossible to access a doctor's appointment.
She said "You call in the morning to make an appointment at literally one minute to 8am and it's impossible to get through, the lines are jammed straight away, everyone is trying to call at the same time and there just aren't enough appointments in the day.
"Then usually you're offered an appointment a week, eight to ten days ahead… the access to appointments is very limited. It's really difficult unless you sound really, really urgent."
Pragya said "I hate to malign the NHS in any way, everyone works incredibly hard. Our local GP seems under a lot of pressure to meet deadlines, so when you do see someone for five to 10 minutes it's very rushed."
'No chance of seeing someone that day'
Olivia Djouadi, 46, from Bromley in south London, where 94% of patients have full access to extended hours appointments. She is self-employed and cares for a disabled teenage son.
"I call for an appointment at 8 o'clock on a Monday morning and can be given an appointment for a couple of weeks time.
"At 8 o'clock, it seems they've booked all the slots for the day. If you are even slightly late, like 8.15, there is no chance of seeing someone that day.
"I've often been given an appointment for a couple of weeks time. I have diabetes and lots of medical needs so I can't really wait a couple of weeks. If I'm concerned, I will often go to the in-house GP at A&E ... and I sit and wait.
"I have a teenager in a wheelchair and work full-time, so I'd have to cancel his school day if I have to wait at A&E to see someone because I might not be back when his transport brings him home from school."
The success stories
A spokesperson for NHS Rushcliffe CCG said it was proud of the extended hours service it provides, through '"vanguard funding".
In 2015, it became one of fifty 'vanguard' sites created and funded by the NHS. The purpose was to bring together hospitals, community services, GPs and care homes to provide extended care.
NHS Herefordshire CCG has been able to offer full extended access, through the GP Access Fund.
Originally called the Prime Minister's Challenge Fund, it became one of twenty-one pilot areas funded in 2015 to provide extended GP hours.
That has enabled Herefordshire to commission a GP Federation to provide three hub sites across the county, to provide seven-day a week service.
'Not everyone can access hubs'
Christine Price from Healthwatch Herefordshire, the independent champion for people who use health services in the county, said though people want convenience of care, how to get to services for those living in rural communities is an issue.
Christine said "People thought their own local GP would be open as part of extended access, but it's not realistic with twenty-four practices across the whole county.
"With limited transport between market towns and rural areas, the reality is not everyone can access services.
"If all patients wanted to use it, it wouldn't have the capacity for them to use it.
"People without money, friends and family nearby struggle to access services outside of their immediate area. It's not there for everyone in reality."
Should the money be spent elsewhere?
Doctors' groups have questioned the government's priority of extended access at a time when there is a critical shortage of GPs.
In the recent British Medical Association's paper, Dr Richard Vautrey, its GP Committee chair, said the government should address "increased demand and unmanageable GP workloads".
The Royal College of GPs said it wants to give patients access to services they need but states there are not enough GPs to provide this.
Its chair, Helen Stokes-Lampard, has called for funding for an extra GP in every practice in England.
Labour's Shadow Secretary of Health and Social Care, Jonathan Ashworth MP has been critical of the handling of the extended access scheme.
He said "This is yet more evidence that the Tories have broken their promises on access to GPs seven days a week.
"The truth is that years of austerity has taken its toll on general practice. We need a serious long term investment plan for primary care."
A spokesperson for the Department of Health and Social Care said it had invested an extra £2.4bn a year into general practice by 2021.
It said alternative data, recorded in May 2018, sourced monthly from Clinical Commissioning Groups, suggests 55% of the population now had access to 8am-8pm GP services. NHS England has declined to release this data.
A spokesman for NHS England said: "The NHS is investing at least £258m this year to offer improved access to general practice, including evening and weekend appointments. This is ahead of schedule with appointments available to more than half the country now, and they will be available across the whole country by October this year."
A spokesperson for the Department of Health and Social Care said it wants everyone to have access to evening and weekend GP appointments and "already millions have benefitted" from the plans.
Wales, Scotland and Northern Ireland
The BBC also analysed similar data from Wales and Scotland. In Northern Ireland, there was no comparable data available.
In Wales, five out of seven Health Boards provided no out-of-hours appointments after 18:30, in data provided by the Welsh government. GPs chose whether to provide 24-hour care for their patients or to transfer responsibility to local Health Boards.
The Welsh government said its figures "show more appointments are available for people at more convenient times".
In Scotland, 3% of patients are registered at a GP practice that has opted in to provide out-of-hours services, in data provided by the Information Services Division (ISD) on behalf of the Scottish Government.
A Scottish Government spokesman said GPs were not contractually required to provide care, and it was the responsibility of local Health Boards.
"Everyone in Scotland has access to out-of-hours services - regardless of where they live," he added.