National Health Service
Each of the four countries of the United Kingdom has a publicly funded health care system referred to as the National Health Service (NHS). The terms "National Health Service" or "NHS" are also used to refer to the four systems collectively. All of the services were founded in 1948, based on legislation passed in 1946, 1947 and 1948, by the Labour Government that had been elected in 1945 with a manifesto commitment to implement the Beveridge Report recommendation to create "comprehensive health and rehabilitation services for prevention and cure of disease". NHS Wales was originally part of the same structure as England until powers over the NHS in Wales were firstly transferred to the Secretary of State for Wales in 1969 and thereafter, in 1999, to the Welsh Assembly (now the Welsh Government) as part of Welsh devolution.
Each system operates independently, and is politically accountable to the relevant government: the Scottish Government, Welsh Government, the Northern Ireland Executive, and the UK Government which is responsible for England's NHS. However, some functions might be routinely performed by one health service on behalf of another. For example, Northern Ireland has no high security mental hospitals and thus depends on using hospitals in Great Britain, routinely Carstairs State Mental 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 NHS Foundation Trust. There have been issues about cross border payments.
The systems are primarily funded through central taxation and each provides a comprehensive range of health services, the vast majority of which are free for people legally resident in the United Kingdom and free at the time of use, for emergencies, to foreign nationals. Foreign nationals also receive free treatment if they have been legally resident in the UK for 12 months, have recently arrived to take up permanent residence, are claiming asylum or have other legal resident status. Citizens of European Economic Area nations, as well as those from countries with which the UK has reciprocal arrangements, are also entitled to free treatment by using the European Health Insurance Card. Foreign nationals may be subject to an interview to establish their nationality and residence status, which must be resolved before non-emergency treatment can commence. Patients who do not qualify for free treatment are asked to pay in advance, or to sign a written undertaking to pay.
Taken together, the four National Health Services in 2015-16 employed around 1.6 million people with a combined budget of £136.7 billion.
Although there have been increasing policy divergence between the four systems there is very little evidence linking these policy differences to a matching divergence of performance. It has been suggested that this is because of the uniform professional culture. There are national terms and conditions of employment across the UK, regulation of clinicians is performed on a UK basis and the health trades unions operate across the UK. But of course it does not help that, as Nick Timmins noted "Some of the key data needed to compare performance – including data on waiting times – is defined and collected differently in the four countries." 
For details see:
- History of the National Health Service (England)
- History of NHS Scotland
- History of NHS Wales
- Healthcare in the United Kingdom
- Scottish Government Health and Social Care Directorates
- British Medical Association
- Royal College of General Practitioners
- Gibraltar Health Authority
- "Let Us Face the Future: A Declaration of Labour Policy for the Consideration of the Nation". Labour Party. 1945. Retrieved 3 March 2013.
- Beveridge, William (November 1942). "Social Insurance and Allied Services" (PDF). HM Stationery Office. Retrieved 3 March 2013.
- The Transfer of Mentally Disordered Patients – Guidance on the transfer of mentally disordered patients detained under the Mental Health (NI) Order 1986 to and from Hospitals in Great Britain – August 2011
- "Breakdown of cross-border agreements is costing English trusts millions". Health Service Journal. 14 February 2008. Retrieved 19 January 2016.
- "NHS charges for people from abroad". Citizens Advice. Retrieved 2010-11-16.
- "Bilateral healthcare agreement countries". UK Department of Health. Retrieved 2011-07-22.
- "10 truths about Britain's health service". Guardian. 18 January 2016. Retrieved 19 January 2016.
- Bevan, Gwyn; Mays, Nicholas (11 April 2014). "The four health systems of the UK: How do they compare?". Nuffield Trust. Retrieved 2 February 2016.
- "Outcomes in EHCI 2015" (PDF). Health Consumer Powerhouse. 26 January 2016. Retrieved 27 January 2016.
- Timmins, Nick. "The four UK health systems: Learning from each other,". Kings Fund. Retrieved 2 February 2016.
- Gorsky, Martin. "The British National Health Service 1948–2008: A Review of the Historiography," Social History of Medicine, Dec 2008, Vol. 21 Issue 3, pp 437–460
- Hacker, Jacob S. "The Historical Logic of National Health Insurance: Structure and Sequence in the Development of British, Canadian, and U.S. Medical Policy," Studies in American Political Development, April 1998, Vol. 12 Issue 1, pp 57–130
- Rivett G C From Cradle to Grave – the first 50 (65) years of the NHS. King's Fund, London, 1998 now updated to 2014 and available at www.nhshistory.co.uk
- Stewart, John. "The Political Economy of the British National Health Service, 1945–1975: Opportunities and Constraints," Medical History, Oct 2008, Vol. 52 Issue 4, pp 453–470
- Valier, Helen K. "The Manchester Royal Infirmary, 1945–97: a microcosm of the National Health Service," Bulletin of the John Rylands University Library of Manchester, 2005, Vol. 87 Issue 1, pp 167–192
- Webster, Charles. "Conflict and Consensus: Explaining the British Health Service," Twentieth Century British History, April 1990, Vol. 1 Issue 2, pp 115–151
- Webster, Charles. Health Services since the War. 'Vol. 1:' Problems of Health Care. The National Health Service before 1957 (1988) 479pp
- NHS Choices official website for England's NHS
- Health and Social Care in Northern Ireland official website for Health & Personal Social Services in Northern Ireland
- NHS Scotland official website for NHS Scotland
- Health in Wales official website for NHS Wales
- Birth of the national Health Service BBC archive collection of programmes and documents