Family doctors have been treated with astonishing neglect, shadow health secretary Jonathan Ashworth claimed as Labour promised to give GPs "the resources and support they need".
He said GPs were overworked and underfunded and struggling to cope in the face of rising needs from patients.
Labour said analysis of data from more than 800,000 patients in England suggested a marked worsening of access to GP surgeries.
Mr Ashworth promised that Labour would ensure that GPs are able to provide better and more accessible services, but the party has not set a specific figure for increased funding for practices.
In its election manifesto Labour promised £37 billion for the NHS over five years, paid for by increased corporation tax and income tax hikes for top earners.
The latest GP Patient Survey showed overall satisfaction with GPs remains high, with 85% of people rating their experience as good. Some 92% also had confidence and trust in the last GP they saw.
But Labour's analysis of the figures, published in July, showed a 9% increase in patients finding it "not very easy" or "not at all easy" to get through to their GP surgery by phone, along with a 10% fall in patients who found it "very easy" or "fairly easy" to do so.
According to the analysis there was a fall of almost 10% in patients who were "always or almost always" able to see or speak to their preferred GP and a 7% increase in patients waiting "a week or more later" until they actually saw or spoke to a doctor or nurse.
Mr Ashworth said: "This research exemplifies just how hard it is becoming to see a GP in Tory Britain, with patients' overall experience of their GP services getting drastically worse.
"Overworked and underfunded GPs are struggling to cope with rising needs from patients. Across the country GPs and practice staff are working to keep the service running in the face of astonishing neglect from Theresa May and her ministers.
"The British public deserves better. Labour would give GPs the resources and support they need to provide better and more accessible services for patients."
A Department of Health spokeswoman said: "GPs are the absolute bedrock of the health service which is why we've backed them with an extra £2.4 billion of funding for general practice and 5,000 more GPs by 2020.
"Patients deserve to be able to get the right care at the right time for them and 17 million people are already able to make a routine appointment with a GP at evenings and weekends."
British Medical Association GP executive committee member Dr Gavin Ralston, said: "The worsening state of general practice is a direct result of years of underinvestment, as the failure to address rising patient demand has pushed services to breaking point and left GPs worryingly overstretched.
"The Government must commit to their promises outlined in the five year forward view and urgently address the recruitment and funding crisis in general practice in order to protect services and ensure that patients get the appropriate level of care they need and deserve."