More than a quarter of a million extra GP appointments will be available after the NHS ordered surgeries to stop 'half-day' closing.
Around 700 GP practices, or a tenth of England's total number, are currently thought to shut for part of the week, health bosses have said.
A small number of surgeries are even opening for just 15 hours per week, according to the NHS.
Half-day closures have meant that more than an estimated one million hours of GP time could have been lost last year.
As part of the NHS Long Term plan, practices will now have to seek permission from local health authorities to shutter during working hours - or risk losing funding worth more than £40,000 per business.
Dr Nikki Kanani, acting director of NHS primary care, said GPs will also be made to create more appointments before 8am and after 6.30pm.
She said: "By curbing half day closures we will be freeing up hundreds of thousands of appointments at a time when we know it can sometimes be tricky to see your GP.
"Whilst occasionally practices need to close for training that ensures the up to date skills of family doctors, our changes aim to further reduce regular half day closures and improve the availability of appointments across core hours in the week, supporting the best possible patient access in primary care."