David Cameron is under fresh pressure after a poll put the party on just 27% - one of its lowest ratings of recent years.
According to the Opinium research for the Observer, Ukip is just 10 points behind on 17% after luring voters away from the Tories and Labour.
It also found the Prime Minister's personal rating dropped 8% in a fortnight to 18%.
The latest study comes after a poll of marginal constituencies on Saturday suggested Labour would scoop 93 seats from the Conservatives and take the keys to No 10 if a general election was held on Monday.
Senior figures have this weekend set out their agenda for trying to restore the party's fortunes. Former Defence Secretary Liam Fox criticised "multiple taxation of the same money", describing it as an "iniquity that creates the wrong pattern of behaviour". He said: "We pay tax on our income. Then if we save we pay tax again. If we invest in businesses or property and try to move our money, we will be hit by capital gains tax or stamp duty. Finally, if we have the audacity to die, we get the indignity of inheritance tax."
Theresa May fuelled speculation that she holds leadership ambitions with a speech to Tory grassroots that ranged across industrial policy, banking and the economy as well her usual turf of home affairs. She also reached out to the right out the party with a promise that a Conservative government would scrap the Human Rights Act and could go further by pulling out of its European obligations on rights altogether.
At the conservativehome website's Victory 2015 conference, the Home Secretary said the party must "consider very carefully our relationship" with the European Court of Human Rights (ECHR), suggesting it was restricting Britain's ability to act in the national interest. Mrs May said she expects the Conservative's public sector reform agenda to "become even more radical" and could include allowing companies to make a profit delivering frontline services.
Meanwhile, Conservative MP Sarah Wollaston warned the Prime Minister he was "running out of time" to tackle problems with his "posh" top team.
In a series of tweets the backbencher insisted she was loyal to the leader but suggested his closest allies were yes men.
She wrote: "Inner circle still look far too posh, male & white & Cameron is running out of time to fix it. I consider myself a Cameron loyalist; he is the best person for the job but should listen to critical friends. I am a Cameron loyalist but he needs to change his inner circle which just seems to be telling him what he wants to hear."