The biggest nurse strike in a generation is expected to take place after thousands of healthcare workers voted for industrial action earlier this week.
Unions led by the Royal College of Nursing (RCN) are protesting over a pay award earlier this year of £1,400 for most NHS workers, with the RCN calling for a 15% pay rise.
The government and hospital trusts have said they will try and keep the NHS functioning but health experts have warned critical appointments will have to be cancelled.
It is expected around half of the hospital trusts in England, all the trusts in Scotland and Northern Ireland and all but one in Wales will be impacted.
When is the nurse strike?
Although no date has been set yet for the strike, it is believed it will happen before the end of the year.
The RCN's mandate for strike action runs until to May, six months after the ballot.
What was on the ballot?
The core issue is pay. The RCN claims nurses have had a 20% real terms pay cut since 2010 due to years of below-inflation pay rises.
They say the recent 5% pay rise offered by the government equates to a pay cut with inflation above 10%.
They are calling for a 5% above-inflation pay rise, which would be around 15%.
What has the royal college of nursing said?
RCN General Secretary & Chief Executive Pat Cullen said the vote was a "defining moment in our history."
She said: "Anger has become action – our members are saying enough is enough. The voice of nursing in the UK is strong and I will make sure it is heard. Our members will no longer tolerate a financial knife-edge at home and a raw deal at work."
She called on the forthcoming fiscal statement from the government to be used to address nurses' anger.
They also said the public backed the industrial action.
What happens next?
The government is keen to prevent strikes and both sides claim they want to talk but neither seems keen to give ground.
Health Secretary Steve Barclay said he held "cordial" talks with union leaders on Thursday.
But it is understood the talks were more focused on patient safety during the strikes rather than averting them all together.
The government is likely to keep trying to call off the strike in the coming weeks, while the RCN will settle on a date for the industrial action.
Which NHS trusts are striking?
All NHS trusts in Scotland and Northern Ireland are taking part, and only the Aneurin Bevan Health Board covering the counties around Newport and Cwmbran will not take part in Wales.
In England around half of health trusts are taking part.
In order for a strike to be approved more than 50% of members need to take part in the ballot, and the RCN claims this is the reason large numbers of trusts in England are not taking part.
Imperial College Healthcare NHS Trust
Guy’s and St Thomas’ NHS Foundation Trust
Great Ormond Street Hospital for Children NHS Foundation Trust
Hounslow and Richmond Community Healthcare NHS Trust
St George’s University Hospitals NHS Foundation Trust
Kings College Hospital NHS Foundation Trust
Royal Marsden NHS Foundation Trust
Tavistock and Portman NHS Foundation Trust
University College London Hospitals NHS Foundation Trust
NHS North Central London ICB
NHS South West London ICB
Kent Community Health NHS Foundation Trust
East Sussex Healthcare NHS Trust
University Hospitals Sussex NHS Foundation Trust
South East Coast Ambulance Service
Sussex Community NHS Foundation Trust
Sussex Partnership NHS Foundation Trust
Queen Victoria Hospital NHS Foundation Trust
NHS Kent and Medway ICB
NHS Surrey Heartlands ICB
Southern Health NHS Foundation Trust
Oxford University Hospitals NHS Foundation Trust
Portsmouth Hospitals NHS Trust
University Hospital Southampton NHS Foundation Trust
South Central Ambulance Service NHS Foundation Trust
Solent NHS Trust
Royal Berkshire NHS Foundation Trust
Oxford Health NHS Foundation Trust
Cornwall Partnership NHS Foundation Trust
Devon Partnership NHS Trust
South Western Ambulance Service NHS Found Trust
Dorset Healthcare University NHS Foundation Trust
Gloucestershire Hospitals NHS Foundation Trust
North Bristol NHS Trust
Torbay and South Devon NHS Foundation Trust
University Hospitals Plymouth NHS Trust
University Hospitals Bristol and Weston NHS Foundation Trust
Dorset County Hospital NHS Foundation Trust
NHS Blood and Transplant (NHSBT)
Gloucestershire Health and Care NHS Foundation Trust
Royal Devon University Healthcare NHS Foundation Trust
Avon and Wiltshire Mental Health Partnership NHS Trust
Great Western Hospitals NHS Foundation Trust
Salisbury NHS Foundation Trust
University Hospitals Dorset NHS Foundation Trust
Somerset NHS Foundation Trust
Royal Cornwall Hospitals NHS Trust
Royal United Hospitals Bath NHS Foundation Trust
NHS Bath, North East Somerset, Swindon and Wiltshire ICB (BSW Together)
NHS Devon ICB (One Devon)
NHS Dorset ICB (Our Dorset)
NHS Gloucestershire ICB (One Gloucestershire)
Midlands Partnership NHS Foundation Trust
Herefordshire and Worcestershire Health and Care NHS Trust
The Royal Orthopaedic Hospital NHS Foundation Trust
Worcestershire Acute Hospitals NHS Trust
Shropshire Community Health NHS Trust
University Hospitals Birmingham NHS Foundation Trust
Birmingham Women’s and Children’s NHS Foundation Trust
Robert Jones and Agnes Hunt Orthopaedic Hospital NHS Foundation Trust
Dudley Integrated Health and Care NHS Trust
NHS Birmingham and Solihull ICB (BSol ICB)
NHS Black Country ICB
East Midlands Ambulance Service NHS Trust
NHS Derby and Derbyshire ICB (Joined Up Care Derbyshire)
NHS Nottingham and Nottinghamshire ICB
Derbyshire Healthcare NHS Foundation Trust
Northamptonshire Healthcare NHS Foundation Trust
Derbyshire Community Health Services NHS Foundation Trust
Nottinghamshire Healthcare NHS Foundation Trust
Nottingham University Hospitals NHS Trust
Kettering General Hospital NHS Foundation Trust
Cambridgeshire and Peterborough NHS Foundation Trust
Norfolk and Norwich University Hospitals NHS Foundation Trust
Cambridge University Hospital NHS Foundation Trust
Royal Papworth Hospital NHS Foundation Trust
East Suffolk and North Essex NHS Foundation Trust
Norfolk Community Health and Care NHS Trust
Norfolk and Suffolk NHS Foundation Trust
Cambridgeshire Community Services NHS Trust
Hertfordshire Community NHS Trust
West Suffolk NHS Foundation Trust
NHS Hertfordshire and West Essex ICB
NHS Mid and South Essex ICB
NHS Norfolk and Waveney ICB
NHS Suffolk and North East Essex ICB
North East Ambulance Service NHS Trust
University Hospitals of Morecambe Bay NHS Foundation Trust
Northumbria Healthcare NHS Foundation Trust
County Durham and Darlington NHS Foundation Trust
Gateshead Health NHS Foundation Trust
The Newcastle upon Tyne Hospitals NHS Foundation Trust
South Tees Hospitals NHS Foundation Trust
North of England CSU (NECS)
Mersey Care NHS Foundation Trust
Tameside and Glossop Integrated Care NHS Foundation Trust
Liverpool Heart and Chest Hospital NHS Found Trust
Lancashire Teaching Hospitals NHS Foundation Trust
The Clatterbridge Cancer Centre NHS Found Trust
The Christie NHS Foundation Trust
Wrightington Wigan and Leigh NHS Foundation Trust
Countess of Chester Hospital NHS Foundation Trust
North West Ambulance Service NHS Trust
Liverpool University Hospitals NHS Foundation Trust
Mid Cheshire Hospitals NHS Foundation Trust
Bridgewater Community Healthcare NHS Foundation Trust
Wirral Community Health and Care NHS Foundation Trust
Midlands and Lancashire CSU
Wirral University Teaching Hospital NHS Found Trust
Liverpool Women’s NHS Foundation Trust
Central Cheshire Integrated Care Partnership
St Helens and Knowsley Teaching Hospitals NHS Trust
Alder Hey Children’s NHS Foundation Trust
The Walton Centre NHS Foundation Trust
Health Education England
NHS Cheshire and Merseyside ICB
NHS Lancashire and South Cumbria ICB
Cheshire and Wirral Partnership NHS Foundation Trust
Yorkshire and the Humber
Sheffield Health and Social Care NHS Foundation Trust
Barnsley Hospital NHS Foundation Trust
York and Scarborough Teaching Hospitals NHS Foundation Trust
Leeds Community Healthcare NHS Trust
Bradford Teaching Hospitals NHS Foundation Trust
Harrogate and District NHS Foundation Trust
The Leeds Teaching Hospitals NHS Trust
Sheffield Teaching Hospitals NHS Foundation Trust
Sheffield Children’s NHS Foundation Trust
NHS West Yorkshire ICB