The Government cannot expect to have a healthy population while underfunding the NHS, Jeremy Corbyn has said, as analysis of data by Labour suggested a marked worsening of access to GP surgeries.
Mr Corbyn, who was visiting a health practice in west London, said his party would "invest more" to reduce the pressure on GPs.
His comments came after shadow health secretary Jonathan Ashworth claimed family doctors have been treated with astonishing neglect, and said they were overworked and underfunded and struggling to cope in the face of rising needs from patients.
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 data from more than 800,000 patients, 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.
During the visit to the surgery, the Labour leader told the Press Association: "We're going to invest more in GP practices and services and invest in nurse training and in GP training because at the moment the pressure is huge on the GPs.
"A lot of the work is actually a consequence of other problems in housing, other problems of stress at home, and that means that the nurse at the practice is dealing of course with medical cases but they are also dealing with a whole load of other things so it is about how we treat and invest in inner city areas."
Labour has not set a specific figure for increased funding for practices, and Mr Corbyn said: "The money will come through taxation and it will cost - and it will cost by raising corporation tax and raising taxes for the very richest in our society.
"We cannot underfund our NHS and expect to have a healthy population."
Mr Corbyn spent more than an hour visiting the Somerset Family Health Practice in Southall, west London, where he spoke to doctors, nurses and councillors from the local area.
He listened to the concerns of practice nurse Shaheena Saeed who told him she loved her job but felt like she was in "purgatory" because of the 1% pay cap.
Mr Corbyn told her: "You're overworked and you're not paid properly for it, and the stress levels must be huge."
Commenting on Labour's analysis of data, Mr Ashworth said patients' overall experience of GP services was "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."