Many doctors' surgeries are closing for extended periods during the week, making it harder for patients to get an appointment with their family GP, it was reported.
The Daily Mail said more than one in four surgeries were closing their doors for one afternoon a week, while others had lunch breaks lasting up to four and a half hours.
Patients' groups criticised the revelation as a "ridiculous situation". Joyce Robins, co-director of Patient Concern, said: "Woe betide you if you get sick on a Wednesday or Thursday afternoon."
Earlier this year a survey for the Mail and over-50s group Saga revealed that as many as two million people have to wait up to three weeks to see a GP.
The Royal College of General Practitioners (RCGP) also claimed that more than 34 million people will this year fail to get an appointment with their GP when they seek one.
The newspaper analysed the opening hours of 944 GP surgeries from 20 clinical commissioning groups - new local health bodies made up of general practices - in areas including London, Manchester, Birmingham, Sheffield, Brighton, Cumbria and Devon.
Some 275 - 29% - shut for lengthy periods during the working week. Of those, 26% closed for one afternoon a week, usually a Wednesday or Thursday, and 3% took lunch breaks of between two and four and a half hours.
Two thirds of the 105 surgeries in Sheffield are shut on a Thursday afternoon, the Mail said, with some closing at 10.20am.
The closures drew scathing criticism from patient groups, who also warned that periodically shutting GP surgeries would put more pressure on already over-burdened accident and emergency units in hospitals.
Ms Robins said: "It's a ridiculous situation given most surgeries have between 10 and 12 GPs working there - you'd think someone could be there during the afternoon. The Government is meant to be encouraging practices to stay open for longer in the evenings but many aren't even open when they should be."
Katherine Murphy, chief executive of the Patients Association, urged the Government to address the issue to ensure that patients can get appointments with their GP during core hours between 8am and 6.30pm.
She said: "It is ultimately the patients who will suffer and they will continue to present themselves at the already overstretched A&E if they are not able to access GP services when they need it."
Dr Marueen Baker, chairman of the RCGP, said the Mail's findings were at odds with what GP members told them, saying doctors were working longer hours to provide more care for patients.
NHS England told the newspaper: "GP practices must open for their contracted hours. This is non-negotiable."