Support for Labour under Gordon Brown could drop to 29%, while the Tories led by David Cameron would attract 42%, an opinion poll suggests.
The poll suggests Cameron's support has grown
With Mr Brown expected to take over as PM, the ICM/Guardian phone poll asked 1,000 adults at the weekend which party - with a named leader - they preferred.
The same question a month ago suggested Labour under Brown would gain 31% and Conservatives under Cameron 39%.
The Lib Dems under Sir Menzies Campbell dropped to 17% from 19% a month ago.
When asked about voting intentions - regardless of leaders - the poll suggests 40% of respondents supported the Conservatives, up three points on January.
Support for Labour was static on 31%, and the Liberal Democrats lost 4 points to drop to 19%.
* ICM interviewed 1,000 adults aged 18 and over by telephone between February 16 to 18.