Just 7% of Tory activists believe David Cameron will secure victory in 2015 in a new poll likely to fuel unease among already restive party members.
And Labour would scoop 93 seats from the Conservatives and take the keys to No 10 if a general election was held tomorrow, according to a separate poll of marginal constituencies.
Overall, Labour would gain 109 seats, taking them to a total of 367 MPs and giving them a majority of 84, the study found. Labour also stand to gain two seats – Cambridge and Leeds North West – where they are currently third.
The research, carried out by Lord Ashcroft, who has previously donated millions to Tory coffers, found there would be an 8% swing to the Opposition in the most closely contested seats.
Nearly 20,000 voters in 213 constituencies were polled for the study which found Labour would win 93 of the 109 most marginal Tory seats, with the biggest swing to the Opposition in the Thames Estuary and the Midlands.
Based on the research, the Lib Dems would lose 17 constituencies in England and Wales to their coalition colleagues and 13 to Labour.
Lord Ashcroft announced the findings on Saturday at the Victory 2015 conference being staged by website conservativehome.
He said: "I don't want to see a Labour majority of four, let alone 84, but I hope this puts the challenge into some sort of perspective. We have a long way to go to hold onto the seats we gained last time, let alone pick up many more. But things are slightly less grim than the headline polls suggest, and we have everything to play for."
Of those voters defecting from the Tories, 36% would vote Ukip, 17% to Labour or the Lib Dems, and 44% said they did not know or would not vote.
Tory minister Nick Boles said Friday night that the party had "screwed up" in the Eastleigh by-election but warned that it must not swing to the right after the drubbing.
Anthony Wells at UK Polling Report said in a blogpost that he believed the results of the marginal poll were "not particularly surprising – a big swing from Con to Labour, the Liberal Democrats collapsing where they are against Labour but more resilient against the Conservatives.
"It is good to have solid data to back up what I was only assuming was happening in the marginal seats though!"
He said the data was in fact the most interesting when applied to the Lib Dem's electoral chances. "When PoliticsHome asked the two stage voting intention question structure [ie, how would you vote, then how would you vote in your own constituency] back in 2009 it found the Lib Dems did 10 points better in LD-Con seats when people were prompted to think about their own constituency (and conseqently was actually quite a good pointer to how well they’d do at the 2010 election – it had them getting 55 seats, compared to the 57 they actually got).
"Overall, if this poll was reflected at the next general election – still two years away remember- it would leave the Lib Dems with around 25 seats, a very sizeable loss, but not the complete wipeout that some have predicted, feared or hoped for."
Bookmakers William Hill are offering 7/2 odds that the Lib Dems will remain in government after the next election - in coalition with Labour.
"It is ironic that although they are facing a number of crises and scandals, the Lib Dems are still well placed to be king-makers at or after the next General Election, with or without Nick Clegg," said William Hill's spokesman Graham Sharpe.
The bookmaker is offering odds of 6/5 on it being a Labour government in 2015,11/8 on a hung parliament and 7/2 on a Tory government. Ed Miliband is 4/5 to mb the next prime minister.