NHS nurses are to strike for two days in December in a dispute over pay and patient safety.
Members of the Royal College of Nursing (RCN) will take industrial action on 15 and 20 December across England, Wales, and Northern Ireland.
In Scotland, industrial action is being paused while pay negotiations continue.
The strike ballot among more than 300,000 members of the RCN was the biggest in the union's 106-year history.
The union has demanded its members receive a pay rise of at least 17%, adding that years of low pay is "pushing nursing staff out of the profession and putting patient care at risk".
Nurses had given the government a deadline to open "detailed negotiations" and threatened to announce strike dates for December.
RCN general secretary Pat Cullen said: "My offer of formal negotiations was declined and instead ministers have chosen strike action.
"Nursing staff have had enough of being taken for granted, enough of low pay and unsafe staffing levels, enough of not being able to give our patients the care they deserve."
Pay demand 'not affordable'
The health secretary praised the hard work and dedication of nurses, and expressed his deep regret that some will be taking industrial action.
Steve Barclay said: "These are challenging times for everyone and the economic circumstances mean the RCN's demands, which on current figures are a 19.2% pay rise, costing £10bn a year, are not affordable."
The RCN's demanding an increase based on the RPI inflation rate (which was 14.2% in October) plus 5%.
In England and Wales, NHS staff have seen an average rise of 4.75% this year, in Scotland the offer was a flat rate of just over £2,200, while in Northern Ireland no pay award can be approved without an Executive in place.
Chancellor Jeremy Hunt - who previously held the post of health secretary - said he has a "great deal of sympathy" for nurses struggling with the cost of living, but insists the best way to help them is to bring inflation down.
Prime Minister Rishi Sunak has also called the pay demands "obviously unaffordable".
Data from the London School of Economics found salaries of experienced nurses have declined by 20% in real terms over the last 10 years. This means nurses are effectively working one day a week for free.
That mirrors recent research by the health charity Nuffield Trust, which said NHS staff pay remained lower in real terms in 2021/22 than it was in 2010/11.
'Something needs to change'
RCN director Patricia Marquis told Sky News nursing pay has fallen behind during the last decade and the action was nurses telling ministers "something needs to change".
"Our members are sending a very loud message to the government that things need to change for nurses in their NHS," she said.
"We got a pay award this year of £1,400 which may sound a lot to people, but actually nursing pay has fallen behind over the last 10 years by around the rate of inflation plus 5% - so our members are hugely disappointed that they didn't get anywhere near what they needed to take their salaries back to the level they were 10 years ago.
"What is really worrying them is the impact that's having on patient care. There aren't enough nurses and nursing staff to deliver the care that's needed. So patients are waiting too long for their operations, they are waiting for ambulances and they are waiting for beds, and it just is not safe for patients any longer, and nurses are saying 'we have had enough, we can't continue, something needs to change'."
NHS vacancies at record high
Nursing vacancies hit a record 47,000 in England between April and June, a rise of a fifth on the year before.
The RCN says 25,000 nursing staff in the UK left the Nursing and Midwifery Council register in the last year.
This summer, MPs from the cross-party Health and Social Care Committee described the staffing issues as "the greatest workforce crisis" in the history of the NHS.
The union blames not just pay, but also heavy workloads.
The RCN is not the only health union threatening strike action.
A ballot among Unison members closes on Friday, and among Unite's NHS members next week.
Midwives and physiotherapists are also voting on taking action, and junior doctors will be balloted in the new year.
Meanwhile, ambulance staff in Scotland are due to walk out on Monday.
Labour blames Tory 'negligence'
Shadow health secretary Wes Streeting blamed the government for failing to negotiate with the RCN.
He said: "Patients already can't get treated on time, strike action is the last thing they need, yet the government is letting this happen. Patients will never forgive the Conservatives for this negligence."
What about the safety of patients?
Unlike strikes in other sectors, some nurses will be exempt from taking part in strike action - called "derogations" - to maintain safe staffing levels and ensure patients are not harmed.
An RCN spokesperson said: "We are committed to ensuring life-preserving service is in place and will be confirming derogations with individual employers in due course."
Nurses could follow the example set in Northern Ireland in 2019, when staff went on strike.
The RCN has described on its website how staffing was managed on three levels:
• complete derogation, with an entire service being staffed like intensive care units
• limited to a Sunday service or Christmas Day service
• limited to a night duty model
Could agency workers replace striking nurses?
The RCN advice is clear: "If you're an agency worker allocated to work at an NHS organisation on a day of strike action, we at the RCN expect that you do not cover that shift.
"You could ask your agency to find you alternative work at an organisation that is not taking strike action, for example a private hospital or care home."
That doesn't mean agency staff have to follow the advice, though - and some shifts can be lucrative.
A recent freedom of information request by Labour showed one in three NHS trusts have paid an agency more than £1,000 for a single shift last year, and one in six trusts paid more than £2,000.