Labour have an 18-point lead over the Tories ahead of the general election when it comes to the NHS, according to Lord Ashcroft.
The former Conservative Party deputy chairman, who surveyed more than 20,000 respondents between 14 and 24 November, found that almost half (47%) of voters thought Ed Miliband's party had the best approach to the health service.
In contrast, the research revealed that only 29% of respondents thought that the Tories had the best approach to the NHS and the survey also found that just 15% of people thought the service has improved in the last five years.
"The debate over the NHS in this year's general election campaign has already become an exchange of insults, doubtful assertions and unreliable statistics of the kind that voters find so edifying," Ashcroft said.
"But despite the noise, both parties are avoiding real discussion of the subject. Being by far the most trusted party on the NHS, Labour have put the health service at the centre of their campaign.
He added: "But they look set to focus on GP appointment times, spending the proceeds of their Mansion Tax and, of course, attacking the Tories' record.
"There is no sign of the harder thinking on the choices needed to make the NHS sustainable in the longer term of the kind that the previous Labour government was prepared to grapple with.
"They know these choices are unpalatable, not least with their own voters, and have decided not to trouble the electorate with them at this stage."
The research also revealed that creating jobs and getting the economy growing (60%), controlling immigration (49%) and improving the NHS (42%) were named the top three concerns for voters.
The findings come after a poll from YouGov for The Sun, which surveyed more than 1,700 people between 12 and 13 January, put Labour on a one-point-leader of the Tories (33% vs 32%) ahead of May's vote, with Ukip on 14% and the Liberal Democrats and The Green Party both on 7%.