The leader of Britain's family doctors has warned that GP services are "under severe threat of extinction" because they cannot cope with the growing demand for care. Practices are forcing patients to endure long waits for appointments, and allowing them too little time with their GP, according to Dr Maureen Baker, who chairs the Royal College of GPs.

In an outspoken intervention, Baker claimed that allocating general practice an ever smaller share of the NHS budget was foolish because GP surgeries were "shoring up the rest of the NHS from collapse" by relieving pressure on hospitals.

"General practice as we know it is under severe threat of extinction. It is imploding faster than people realise and patients are already bearing the brunt of the problem," said Baker, who demanded urgent action to reduce "the huge and historic imbalance in funding".

She added: "For generations GPs have been the bedrock of the NHS and provided excellent care for patients. But we can no longer guarantee a future for general practice as our patients know it, rely on it – and love it."

Surgeries are responsible for about 90% of all patient contact, but general practice only receives 8.39% of the UK's overall NHS budget. That share has been falling since 2003-04, while hospitals have been getting more, despite NHS leaders and ministers agreeing that growing numbers of hospital services need to be delivered elsewhere.

"GPs are doing all they can, but we are being seriously crippled by a toxic mix of increasing workloads and ever dwindling budgets, which is leaving patients waiting too long for an appointment and not receiving the time or attention they need and that GPs want to give them," said Baker.

She urged the governments in Westminster, Edinburgh, Cardiff and Belfast to ensure the NHS's 10,000 GP surgeries, staffed by the UK's 40,000 family doctors, get more money from next month and "wake up to the critical state that general practice is now in". Without that, patients would not get the care that they need and "if this doesn't happen, we have grave concerns for the sustainability of the NHS", added Baker.

Six in 10 (62%) of Britons believe the number of consultations GPs do each day is putting the standard of care they offer patients under threat, according to a ComRes poll of 1,007 adults selected to represent the whole population and commissioned by the RCGP.

While 70% were able to book an appointment within the same week the last time they tried, 28% could not. Worryingly, 40% were concerned about the effect long waiting times would have on their health.

Andy Burnham, the shadow health secretary, said it was unacceptable that any patient had to wait up to a week to see a GP. "This is putting patients at risk and flies in the face of personal promises made by the prime minister. David Cameron is presiding over a serious deterioration in the quality of primary care," said Burnham.

An NHS England spokesman said that the health service had increased the amount going into GP services by a third in real terms since 2002-03. It was giving England's 211 GP-led clinical commissioning groups £250m to provide new primary care and community services and putting another £50m into helping family doctors improve access , including by phone, email and video.

The Department of Health declined to respond directly to Baker's stark warning. It recognised the vital job that GPs do, a spokesman said. "That is why we have cut GPs' targets by more than a third to free up more time with patients and are dramatically increasing trainees so that GP numbers continue to grow faster than the population."

The RCGP says that the NHS needs another 10,000 GPs to provide timely access and high-quality care because an ageing population and rising numbers of people with long-term conditions are producing heavier demand for their services. The coalition has responded by promising to increase the number of GP trainees from 40% of all newly qualified doctors leaving medical school to 50% by 2020.