That could yet see Cameron denied office by a coalition between Labour, with or without the faltering Brown, and the Liberal Democrats, who many analysts see as more natural ideological allies than a Conservative-led coalition.
While Cameron has waged a solid campaign, calling for Britons to vote for change after 13 years of Labour government, he has also been forced to fight off an unexpectedly strong challenge from the Liberal Democrats, traditionally the UK's third party.
That followed a strong performance by Lib Dem leader Nick Clegg in the first of three televised debates between the three main party leaders; the first time such debates have been held in a British election campaign.
But Cameron fought back strongly in the third debate on the subject of the economy with most polls giving him a clear victory over his rivals.
In recent months, commentators have detected a "more terse, zingy" Cameron, compared to the smooth performer to whom Britons have grown accustomed.
"It was a big change from the Cameron of a few months ago who was so maddeningly languid and moderate," the Daily Mail newspaper's Quentin Letts said of one performance.
Anything less than an outright majority would be damaging for Cameron, whose appeal to the Tory faithful has mostly rested in the promise that he would deliver an election victory -- and preferably an emphatic one -- for a party which dominated 20th century British politics.
The 43-year-old has styled himself as a new kind of compassionate Conservative who has modernized his party -- historically a bastion of privilege, wealth and establishment values -- by softening its stance on social issues and broadening its appeal by recruiting more female and ethnic minority candidates.
