The Conservatives say they are ready and waiting to fight a snap election.
David Cameron campaigning in elections earlier this year
Sources close to leader David Cameron say the party has a £10m war chest, a draft manifesto and candidates selected in their top 200 target seats.
The Tories say Gordon Brown, who became prime minister when Tony Blair stood down, should seek his own mandate.
This week's Labour conference has been dominated by speculation that Mr Brown will respond to recent opinion polls by deciding to call an autumn election.
The Conservatives, who hold their annual party conference in Blackpool next week, claim their election planning is ahead of either of the other two main parties.
They insist the polls, which have suggested Labour has bounced back into a sustained lead during Mr Brown's first three months as PM, are more volatile than is being reported.
Conservative sources have told the BBC the party board has met this week to agree measures to impose candidates on the 200 non-priority vacant seats if necessary.
The source said that candidates have been selected and election literature and material already distributed to all their target seats.
'More likely than not'
Mr Brown does not have to call a general election until 2010 but has repeatedly refused to rule out calling a snap election.
He has also said that he is implementing Labour's 2005 election manifesto so does not need to hold an election to get a mandate.
But one minister told the BBC on Wednesday an early election now looked "more likely than not".
Universities Secretary John Denham told the BBC's World at One it would be tempting to hold an election if it meant that rather than having the current 60-odd Labour majority for two years the party could have a 100 majority in Parliament for five years.
And Mr Brown's old Treasury right-hand man and current schools secretary, Ed Balls, told BBC Radio 4's Today programme that it was arguable whether it would be more of a gamble not to call an election now.
The Liberal Democrats have also said they are ready for a snap election, with leader Sir Menzies Campbell telling their party conference last week that they were the "real" opposition and were set to "rattle the cage" of British politics.