Almost half of voters say they would be happy to pay more income tax as long as the money went directly to the NHS, which is facing a £30bn gap in its finances by 2020.

Polling firm ComRes found that 49% of people would be prepared to pay more tax to help fund the health service, one in three (33%) people said they would not be ready to do so, and 18% did not know either way.

However, if only the views of those who expressed an opinion are considered, as many as 60% of people are willing to pay more tax to help the NHS providing its wide range of services; 40% are not.

The public's willingness to pay extra tax to help the NHS has reached its highest level in over a decade amid growing concern about hospitals slipping into the red, waiting lists lengthening and the service becoming unsustainable.

The 49% and 60% figures are the highest seen for either of the methodologies since the early 2000s, just before Tony Blair's government kickstarted a sustained campaign of well above inflation NHS budget increases.

Professor Chris Ham, chief executive of the King's Fund health thinktank, said the increase in people willing to help the NHS financially was likely to be linked to public perceptions that it had started to struggle financially and clinically and because it was so highly valued.

The findings should tell political parties that they should not shy from discussing the money needed to ensure the NHS survives and showed that voters might be more willing to pay extra tax for a specific purpose than MPs usually imagined.

"It's a wake-up call to politicians to be willing to debate the funding of the NHS and to avoid colluding with each other in saying spending can't be raised until deficit reduction has been completed," Ham, who helped advise No 10 on health during 2011, said.

"They may be surprised that the public are willing to support politicians who promise to raise taxes for specific purposes like the NHS."

The findings come as Labour, the Liberal Democrats and the Conservatives are examining possible options for boosting the NHS budget after next May's general election, as experts have warned that it is likely to encounter financial meltdown not long before then.

Mike Birtwistle, an NHS policy expert and founding partner of Incisive Health, which commissioned the poll, said: "The extent of support for higher income taxes to fund health services will make political decision-makers sit up and take notice. We know that debates are raging within all parties about whether to commit to tax increases to pay for the NHS."

ComRes interviewed 2,070 British adults online on 23 and 24 July, with the data weighted to be representative of the entire over-18 population. It asked: "Currently income tax in the UK is between 20p (for those earning £10,000–£41,865) and 45p (for those earning £150,000 or above) for each £1 earned. How much extra, if anything, would you personally be willing to pay in income tax for every £1 you earn each month, to go directly to the NHS?"

Excluding the don't-knows, 25% of the 1,727 respondents said they would be willing to pay an extra penny in the pound. But 35% said they would be willing to pay at least 2p extra, with 14% indicating their support for that amount and another 13% saying they would be prepared to pay an extra 5p.

Dr Kailash Chand, the deputy chair of council at the British Medical Association, who received an OBE for his services to the NHS, said the poll underlined that only improved funding for the NHS from general taxation would close the gap between its budget and that of other leading western nations.

"There have been increasing demands to look at alternative ways of funding the NHS, such as charging drunks for A&E attendances, income generation through private patients treated in NHS hospitals, increasing prescription charges and charging for GP attendances. These 'cosmetic' measures will do nothing to save the NHS from the plight of the £20bn 'Nicholson Challenge', rising demand due to complex medical problems and chronic illness, emerging problems of lack of doctors and nurses in some specialities, overburdened general practices and scores of hospitals gasping for oxygen", said Chand.

The British Social Attitudes survey in 2012 found that 38% were prepared to pay more tax to benefit the NHS and a recent Opinium poll for the Observer put that figure at 44%. Both are lower than the 49% ComRes has just found.

After stripping out the 18% don't-knows, ComRes's finding of 60% willingness to pay more tax is above the 57% the firm found in June in a poll for the Independent.

Liberal Democrat MP Norman Lamb, the care services minister at the Department of Health, said: "These are interesting findings that show how strongly people feel about the NHS. The Liberal Democrats are committed to protecting funding and increasing funding for public services as the economy grows. We will also undertake a thorough review of NHS costs and funding to ensure the long-term sustainability of the health service."

A Conservative health spokesman declined to comment on the findings, simply saying: 'We've taken tough decisions to increase the NHS budget by £12.7 billion over the course of this parliament, allowing the NHS to deal with significant rises in demand.'

Labour declined to respond to the findings.