The Government faced fresh anger over its refusal to accept a recommended 1% pay rise for NHS staff as radiographers went on strike - many for the first time in their career.
Members of the Society of Radiographers across the UK, including Northern Ireland, walked out for four hours at 9am and will work to rule for the rest of the week.
They are the latest group of NHS staff to strike following action last week by midwives, nurses, ambulance crews and other health workers in protest at the Government's controversial decision not to accept a recommended 1% pay rise for all health workers.
The action by diagnostic imaging and radiotherapy professionals was their first strike over pay since the early 1980s, with warnings of further walkouts if the bitter dispute is not resolved.
Picket lines were mounted outside hospitals across the country, including St Thomas', opposite Parliament in Westminster, where dozens of radiographers chanted: "What do we want - a pay rise. When do we want it - now."
Sheila Hassan, the society's president-elect, who works at St Thomas', said she had been "amazed" at the level of support for the strike, and from members of the public.
"Radiographers' pay has been cut by 15% in real terms since 2010 and other terms and conditions have worsened, while our workload has increased.
"People have just had enough. There is also a feeling of disgust that the MPs have accepted a huge recommended pay rise for themselves, but ours is rejected. It's just not fair."
Ohe Amoah-Kusi, 24, who qualified two years ago, said he never thought he would ever be on strike.
"Everyone works really hard in the NHS and care for our patients, so we don't think it is fair for the Government to deny us a pay rise.
"One of my concerns is that the Government will do this again to us in future years unless we make a stand now."
Radiology departments and cancer treatment centres were affected by the strike, although emergency and urgent care continued to be provided.
Richard Evans, the society's chief executive officer, said: "This is the first time since 1982 that radiographers have gone on strike over pay and there is the possibility of more action in the future. The anger that they and other NHS workers feel is very strong.
"The last thing that radiographers want is to hurt the people that they serve. Steps have been taken to minimise the impact on patients. This disagreement between NHS staff and the Government has been going on for a long time and radiographers have lost patience with an employer that they feel does not value the hard work that they do."
The society warned that if there was no improvement in pay, there was a real concern that more radiographers will leave the profession for another career, making current shortages worse.
"Patients will have to wait even longer to be seen than they do now. Also, radiography needs to attract students to replace the people who retire or leave the profession every year. There are fears that if pay continues to fall in value, young people will not consider a career that requires three to four years of intensive training," said the society.
The strike follows a huge turnout at TUC organised protests in London, Glasgow and Belfast on Saturday highlighting the need for workers to be given a decent pay rise.
Union leaders rounded on the coalition for policies they said had led to a real-terms cut for workers since the Government came to power in 2010.
A Department of Health spokesman said: "We are disappointed that trade unions are taking industrial action.
"NHS staff are our greatest asset, and we've increased the NHS budget to pay for over 12,500 more clinical staff since 2010. We cannot afford a pay rise in addition to increments - which disproportionately reward the highest earners - without risking frontline jobs."