People in England would be given the right to a GP appointment within a week, under Liberal Democrat plans.
The party says it would set up a 24/7 hotline for patients to book slots, with those who want to see a doctor face-to-face able to do so.
Leader Sir Ed Davey said too many were struggling to see a GP when needed, leading to missed or delayed diagnoses.
Some were “turning in desperation to our overstretched A&E departments instead”, he added.
The pledge comes ahead of a speech by Sir Ed to party activists this weekend, after the party cancelled its autumn conference following Queen Elizabeth II’s death.
The Lib Dems say they would guarantee GP appointments within seven days by updating NHS England’s constitution – which sets out various waiting time targets for access to treatment.
The party says it would also enshrine the right for people to choose a face-to-face consultation, and for people in “urgent need” to be guaranteed an appointment within 24 hours.
Waiting time rights in the document are generally not enforceable by patients, but it creates legal duties on NHS providers.
The targets have been enforced by fines from NHS commissioners, although these have gradually been withdrawn in recent years due to financial pressures on NHS trusts.
Sir Ed said “far too many people” struggled to get a GP appointment when they needed it, leaving them “waiting anxiously for the care they deserve”.
He added the Lib Dem pledge would “reduce pressure on our hospitals and paramedics, saving crucial time and money elsewhere in the NHS”.
“Patients are suffering from years of neglect under the Conservatives, who have repeatedly broken their promise to recruit more GPs,” he added.
The Lib Dems are also calling on the government to recruit 8,000 extra GPs, and make it more attractive for junior doctors to become GPs once they’ve been trained.
The party also wants more to be done to encourage GPs who have left the NHS to return, including by changing rules that mean doctors can face high tax bills if their earnings go above a pension cap.
Two-week pledge
Under former PM Liz Truss, the government recently announced same-day GP appointments for those that needed them, as part of its NHS England plan for this winter and next.
Unveiling the blueprint, former health secretary Thérèse Coffey promised no-one would have to wait more than two weeks for a routine appointment, reflecting a pledge Ms Truss made during her Tory leadership campaign.
Currently, one in five appointments take longer than this.
Rishi Sunak pledged during his unsuccessful summer leadership campaign against Ms Truss that he would fine patients in England £10 if they miss GP appointments, to help clear Covid backlogs.
But he abandoned the policy after replacing Ms Truss in Downing Street last month, after opposition from GPs.