The National Health Service (NHS) is the umbrella term for the publicly-funded healthcare systems of the United Kingdom (UK). Since 1948 they have been funded out of general taxation. There are four systems, one for each of the four countries of the UK: The NHS in England, NHS Scotland, NHS Wales and Health and Social Care in Northern Ireland. They were established together in 1948 as one of the major social reforms following the Second World War. The founding principles were that services should be comprehensive, universal and free at the point of delivery—a health service based on clinical need, not ability to pay. Each service provides a comprehensive range of health services, free at the point of use for people ordinarily resident in the UK, apart from dental treatment and optical care. In England, NHS patients have to pay prescription charges; some, particularly those receiving state benefits, are exempt.
Each of the UK's health service systems operates independently and is politically accountable to the relevant government: the Scottish Government, Welsh Government, Northern Ireland Executive, and the UK Government, responsible for England's NHS. Since 2013 operational responsibility for the NHS in England has been passed to NHS England. NHS Wales was originally part of the same structure as that of England until powers over the NHS in Wales were first transferred to the Secretary of State for Wales in 1969 and thereafter, in 1999, to the Welsh Assembly as part of Welsh devolution. Some functions may be routinely performed by one health service on behalf of another. For example, Northern Ireland has no high-security psychiatric hospitals and depends on hospitals in Great Britain, routinely at Carstairs hospital in Scotland for male patients and Rampton Secure Hospital in England for female patients. Similarly, patients in north Wales use specialist facilities in Manchester and Liverpool which are much closer than facilities in Cardiff, and more routine services at the Countess of Chester Hospital. There have been issues about cross-border payments.Taken together, the four National Health Services in 2015–2016 employed around 1.6 million people with a combined budget of £136.7 billion. In 2014, the total health sector workforce across the UK was 2,165,043. This broke down into 1,789,586 in England, 198,368 in Scotland, 110,292 in Wales and 66,797 in Northern Ireland. In 2017, there were 691,000 nurses registered in the UK, down 1,783 from the previous year. However, this is the first time nursing numbers have fallen since 2008. Every 24 hours it sees one million patients, and with 1.7 million staff it is the fifth biggest employer in the world.Although there has been increasing policy divergence between the four National Health Services in the UK, it can be difficult to find evidence of the effect of this on performance since, as Nick Timmins says: "Some of the key data needed to compare performance – including data on waiting times – is defined and collected differently in the four countries." Statistics released in December 2017 showed that, compared with 2012-2013, the number of patients in Scotland waiting more than four hours in accident and emergency dropped by 9% (from about 8% of all A&E patients to about 6%), whereas in England that proportion had increased by 155% (from less than 5% of all A&E patients to about 11%). However, since then, Scotland in common with the other three UK nations has experienced increasing pressure in Accident and Emergency departments with lengthening waiting times.When purchasing drugs, the NHS has significant market power that, based on its own assessment of the fair value of the drugs, influences the global price, typically keeping prices lower. Several other countries either copy the UK's model or directly rely on Britain’s assessments for their own decisions on state-financed drug reimbursements.