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 in evenings and at weekends.
Around 40% of patients registered with GPs now have seven-day 8am to 8pm access to GPs, which is defined as full provision by NHS England.
Just over half the population have access to partial provision, which is when a GP practice can offer the minimum of 90 minutes of bookable appointments once a week.
Only two areas offer full provision to GPs for all patients.
Former Prime Minister David Cameron promised that everyone in England would have access to GP services seven-days a week by 2020.
The plans have since been brought forward and 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 shows widespread regional variation.
In Sefton in Merseyside, 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 spokesperson for the Department of Health and Social Care said alternative data, recorded in May 2018, sourced monthly from clinical commissioning groups, suggests 55% of the population now has access to 8am-8pm GP services.
A spokesman for NHS England added: “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.”