The NHS’s future is in danger because its model of care cannot meet the relentlessly growing demand for treatment caused by the ageing population, the service’s top doctor has warned.

Prof Sir Bruce Keogh, medical director of the NHS in England, said that without massive changes to the way the NHS treats patients, including far less reliance on hospitals, the service risked becoming unaffordable and could see its entirely taxpayer-funded status challenged.

In an interview with the Guardian, Keogh said: “If the NHS continues to function as it does now, it’s going to really struggle to cope because the model of delivery and service that we have at the moment is not fit for the future.”

An unprecedented shift of resources and care into GP surgeries was necessary to help the NHS withstand the twin pressures of rising demand and tight budgets, Keogh added, given the increasing numbers of patients turning up at A&E who needed to be admitted to hospital.

“If not, we will get to a place where the NHS becomes unaffordable and we will have to make some very difficult decisions which will get to the very heart of the principle of the NHS and its values. This will open up a whole series of discussions about whether the NHS is fit for purpose, whether it’s affordable, and whether the compact with the citizen of free healthcare for all is sustainable in the longer term.”

But he denied claims by medical bodies such as the Royal College of Nursing and by the Labour party that key NHS services such as accident and emergency, GP surgeries and ambulance services are struggling so much to cope with demand that the service is in a crisis. Waiting times at A&E are at their worst level since the current system of record keeping began in 2004 and three of the 10 ambulance trusts in England have had to declare a critical alert over the winter.

Asked if current pressures constituted a crisis, Keogh replied: “No. Everybody that’s working out there in the NHS knows that they’re under a lot of pressure at the moment. They don’t like the term ‘crisis’ being applied willy-nilly.

“It’s an evocative term which is also provocative and is used too freely for the wrong reasons. It’s a period of unprecedented pressure, of undue pressure. But the NHS is facing very difficult times, yes. The word ‘crisis’ implies that you can’t deal with it,” said Keogh. NHS frontline services “are going through a critical phase” but would recover, he insisted.

Although most A&E units are missing the target of treating 95% of arrivals within four hours, they are still attending to nine out of 10 patients within that time – one of the best performances of any healthcare system in the world, Keogh said. But he conceded that the four-hour target was an accurate barometer of how well health and social care services were performing and currently “the barometer is saying ‘stormy’”.

Keogh said that the NHS would have to undertake a “complete transformation” of the way it operates over the next few years in order to keep itself sustainable. That would require hospital consultants to visit patients in their GP surgery and the sickest patients being given much more time to discuss their health than the usual 10-minute appointment with a family doctor.

In future, many patients will be able to get much of their care, including diagnostic tests and an expanded range of treatments, at their GP surgery to save them having to go to their local hospital.

Providing many more services under one roof would, Keogh said, reduce patients’ frustration at having to undertake appointments in different places. “Too many patients find the NHS fragmented [and] confusing. They find that they get pushed from pillar to post; they feel like a ball in a pinball machine at times.”

But he added that NHS England was confident that the major changes outlined in October in its Five Year Forward View blueprint for the service’s future, including an unprecedented build up of services delivered outside of hospitals, would help the NHS remain viable. The main priority in future would be to keep as many patients as possible out of hospital “dormitories” where they do not want to be and could catch an infection.

Keogh pinpointed the lack of local services such as district nurses, beds in community hospitals and mental health support as a key cause of the ever-rising demand for care from A&E units and for hospitals running out of beds. All those services are “very, very busy” because of the rising number of older people with complex medical needs and therefore have waiting lists.

Andrew Gwynne, the shadow health minister, said: “We have long warned that the collapse of community services would drag down the NHS and that is what we can see now that hospitals have record numbers of older people who can’t be discharged. Labour agrees with Prof Sir Bruce Keogh that a key part of the way to make the NHS affordable and sustainable in this century is to give patients more care where they want it.”

A Department of Health spokesman said: “In common with healthcare systems around the world, the NHS is facing unprecedented demand, but undermining the principle of services being free at the point of use is not the answer. Instead, we are backing the NHS’s plan for the future and have provided an extra £2bn in funding next year to transform out-of-hospital care and meet the needs of an ageing population.”