Theresa May has overtaken Boris Johnson in the race to become the next prime minister, according to polling.
The Home Secretary and former London mayor are among leading Tories who are expected to spend the day drumming up support for potential leadership bids ahead of nominations opening on Wednesday.
But a surge in support for Mrs May has seen her leap ahead of the bookies' favourite to win the contest to replace David Cameron, research for The Times found.
The Cabinet minister is favoured by 31% of Conservative voters against 24% for Mr Johnson, according to the YouGov poll.
Chancellor George Osborne, meanwhile, said it was clear he could not provide the unity the party needed as he ruled himself out of standing in the contest.
Work and Pensions Secretary Stephen Crabb and Business Secretary Sajid Javid are reportedly considering standing on a joint ticket.
Other contenders who are considering throwing their hat into the ring include Education Secretary Nicky Morgan and former frontbencher Liam Fox.
Despite once saying the Health Secretary brief was his "last big job in politics", Jeremy Hunt is also reported to be among those considering a shot at the leadership.
Prominent Brexit campaigners Andrea Leadsom, minister for energy and climate change, and work and pensions minister Priti Patel are expected to stand, according to reports.
Nominations will open on Wednesday and close the following day, with a new prime minister and Conservative leader in place by September 2 at the latest.
Mr Johnson and Mrs May have been urged by Cabinet minister Justine Greening to form a "united leadership" to help bring together a country left divided after the poll.
Mr Osborne told The Times today that the EU referendum had left him a divisive figure.
He said: "It isn't in my nature to do things by half-measure and I fought the referendum campaign with everything I've got. I believed in this cause and fought hard for it."
"So it is clear that while I completely accept the result, I am not the person to provide the unity my party needs."