Patients are being forced to wait for as long as three weeks to see their GP after practices have reduced their evening and weekend appointments, Labour said.
There has been a 5.7 per cent drop in the number of GP surgeries offering appointments out of normal working hours, according to research conducted by the party.
Last year half of England’s primary care trusts reported a decrease in the number of GP surgeries offering care outside normal working hours.
The figures suggest that people are turning to accident and emergency wards for help for their ailments after one million extra visits to emergency units were recorded last year in comparison to 2009-10.
Shadow health secretary Andy Burnham accused David Cameron of breaking his pre-election pledge that all patients would be able to see their local GPs until “8pm seven days a week”.
Mr Burnham said: “David Cameron made a lot of promises on the NHS and one by one we are seeing these promises broken.
“The combination of the financial challenge with the biggest ever reorganisation of the NHS has served to severely destabilise the NHS at a critical moment.
“We can demonstrate that it is having a direct impact on standards of patient care.”
He said that more than 1,300 patients have contacted the party with concerns about the NHS.
Of these, around 50 have complained about their local GP services, with many reporting that it takes them between two and three weeks to see their doctor.
Labour contacted 91 of England’s 151 PCTs and found that 56 per cent of them reported a decrease in the number of surgeries offering extended opening hours.
The worst affected areas are Hartlepool - where 31 per cent of surgeries are operating a reduced service - and Newcastle and Haringey PCTs which both reported that a quarter of practices are reducing opening hours.
The research, dubbed The Doctor Won’t See You Now, also found that accident and emergency wards in 46 NHS trusts are not meeting the maximum waiting time of four hours.
Mr Burnham said the data showed that 12 NHS walk-in centres have closed down across England, adding: “This all builds the pressure on GP appointments.”
Royal College of Nursing executive director of nursing and service delivery Janet Davies said: “To deliver a truly patient-centred service people need to know that they can access a full range of health services locally within their GP practice at a convenient time. These findings are of concern and patients need to know why appointments are being restricted in this way.
“The irony is that at a time when the NHS should be trying its hardest to keep people out of hospital, and helping them in the community, pressure is being piled on already overstretched hospitals.”
A Conservative spokesman said: “It is more than a bit rich for the Labour Party to lecture this government on access to GPs out of hours when it was their disastrous GP contract which meant that 90 per cent of surgeries stopped offering this service altogether.”