Tens of thousands of British nurses and ambulance service staff have walked off the job as part of a pay dispute, in the National Health Service's (NHS) largest strike ever. 

Following the industrial action on Monday local time, nurses will also walk out on Tuesday, ambulance staff on Friday, and physiotherapists on Thursday, making the week likely the most disruptive in the NHS's 75-year history, its medical director, Stephen Powis, said.

Health workers are demanding a pay rise that reflects the worst inflation in Britain in four decades.

The government says it cannot afford it, and the move would only cause more price increases, making interest rates and mortgage payments rise further.

"The government needs to listen and discuss pay rather than just saying the NHS doesn't have money," said nurse Ethna Vaughan, who was part of a demonstration outside St Thomas' Hospital in central London.

About 500,000 workers, many from the public sector, have been staging strikes since last summer, adding to pressure on Prime Minister Rishi Sunak to resolve the disputes and limit disruption to public services such as railways and schools.

The Royal College of Nursing (RCN) trade union wrote to Mr Sunak over the weekend, asking him to bring the nursing strike "to a swift close" by making "meaningful" pay offers.

A spokesperson for Mr Sunak said there were no plans for the prime minister to get involved in the talks, adding: "We want to keep discussing how we can find a path forward with the unions."

"We've got one of the busiest winters we have ever had with record levels of funding going into the NHS to try and manage services," Maria Caulfield, the minister for mental health and women's health strategy, told Sky News.

"So every per cent of a pay increase takes money away."

'It looks like a very bleak future'

The NHS is under extreme pressure, with millions of patients on waiting lists for operations and thousands of people each month failing to receive prompt emergency care.

The RCN says a decade of poor pay has contributed to tens of thousands of nurses leaving the profession — 25,000 just last year — with the severe staffing shortages impacting patient care.

"We've got to look at the future, and that's what this is all about … it looks like a very bleak future," said nurse Rebecca Cosgrave, who was also at the demonstration at St Thomas' Hospital.

"A lot of people have left the profession already because they're so disillusioned," she said, while describing how poor pay was making it harder to recruit staff.

The RCN initially asked for a pay rise of 5 per cent above inflation. It has since said it could meet the government "half way", but both sides have failed to reach an agreement despite weeks of talks.

Meanwhile, thousands of ambulance workers represented by the GMB and Unite trade unions are set to strike in their own pay dispute. Both unions have announced several more days of industrial action.

Not all ambulance workers will strike at once and emergency calls will be attended to.

In Wales, nurses and some ambulance workers have called off strikes planned for Monday as they review pay offers from the Welsh government.

Reuters