Out-of-hours GPs are being left to care on their own for up to half a million patients, it has been reported.
Cost-cutting NHS chiefs are routinely assigning just one family doctor to districts that stretch over hundreds of square miles, Mail Online said.
A third of primary care trusts, which manage GP services, have slashed night and weekend spending over the past 12 months, it added.
The Mail said the standard of out-of-hours care had been under scrutiny since 2004 when a new contract enabled GPs to opt out of evening and weekend duties. Now only one in four works out of hours.
Many trusts have since outsourced the cover to private firms who hire locum - or temporary - doctors to fill the shifts, it added.
Using the Freedom of Information Act, the Mail asked every PCT in England a series of questions about out-of-hours cover.
Of the 90 that responded, 35 had slashed their out-of-hours budgets in the past year. The average cut was 10%. And 11 trusts employed only one doctor at night to cover between 180,000 and 535,000 patients.
The Mail said that in Cornwall, some nights have seen one GP looking after 535,000 patients. In Mid Essex just one doctor is in charge of 370,000 between 7pm and 8am. And after axing one of its two doctors, North East Essex has the same cover for the 325,000 patients on its books.
A Department of Health spokeswoman said: "A survey of patients in June this year found that almost two thirds said the time it took to get care from their GP service outside working hours was 'about right'. Two thirds of patients also described their experience of out of hours GP services as 'good', while confidence and trust in the doctor the patient saw was generally high. There is a clear legal requirement on the local NHS to make sure the right, high quality out of hours services are in place, as well as clear quality requirements of those services. If they are not met, the local NHS should take action to improve the local service."
A spokesman from Serco, the private firm which runs out-of-hours cover in Cornwall, told the Mail there were a "limited" number of occasions in the past year when just one GP was on call. He added that Serco now ensured there were at least two GPs on call at night to cover all of the county's 1,316 square miles, and that in addition at least five nurses and paramedics are on duty in cars.