Gordon Brown's fears for the UK economy will be behind any decision to call an early election, former chancellor Ken Clarke has said.
Mr Clarke was chancellor in John Major's government
The Tory MP told the party's conference there was no constitutional reason for Mr Brown to go to the country, nor would it be in the national interest.
Mr Clarke said Mr Brown believed if he did not go now, it would be too late.
Speculation has been growing for weeks that Mr Brown is about to call a general election.
He does not have to hold an election until 2010 - but Labour's continued lead in the opinion polls has led to speculation he will go early. Asked for a likely date, Mr Brown has repeatedly said he is "getting on with the job".
Mr Clarke, who was Mr Brown's predecessor as chancellor from 1993 to 1997, told the conference: "If he calls an election next week, it will not be in the national interest.
"It will not be anything constitutional about a mandate - he doesn't constitutionally need an election for almost three years.
"It will be because, in my opinion, he is so worried about the outlook for the British economy that he thinks if he doesn't go now, it will be too late ever again," he said.
It follows the Conservative former foreign secretary Sir Malcolm Rifkind's comments that a snap general election would be a "constitutional outrage".
Mr Clarke has been heading up a "democracy task force" and outlined proposals to strengthen the role of the House of Commons and Cabinet.
He repeated calls for a ministerial code to ensure government is open and accountable, to circulate papers before Cabinet meetings to allow for proper discussions of policy, and to restore the Commons' powers to hold government to account.
He also said Mr Brown had already "bounded onto" the "sofa-style of government" he said was created by his predecessor Tony Blair - which Mr Clarke blames for causing immense damage to politics.
He also warned Tory leader David Cameron that the public wanted a strong government - not a government that did "short-term popular things".
He told the conference: "I worked with Margaret Thatcher, we never did any popular things as policy at all.
He added: "We argued about what was best to do to tackle the problems based on the convictions that we knew we shared when we were in office. That is the only type of government for which the British people will have respect."
Both the Conservatives and the Liberal Democrats have said they are ready for an autumn election.