Gordon Brown does not have a mandate to run the country, David Cameron has said.
The Conservative leader said Tony Blair is the only member of the Labour party that has been given the right to govern by the British public, and Gordon Brown "will know [this] in his heart".
And the Mr Cameron would welcome the chance for an early general election when Mr Blair steps down in the coming year.
"I would love to have an early election, because it is this government that is putting up the cost of living, that is wrecking the health service, that is failing to reform education, that is sending social mobility backwards," the Tory leader told Today.
"The first step has got to be getting rid of the government."
Mr Blair said he would not stand for a fourth term as prime minister while campaigning in the 2005 general election - but said he would serve a full term.
In September last year, however, the prime minister said he would step down within 12 months, and this means whoever replaces him does not have a mandate, according to the Tory leader.
"Frankly I don't think that anyone except Tony Blair has a mandate because he said that he would serve a full term in office," Mr Cameron said.
"When he goes, his successor, I suspect Gordon Brown, will know in [his] heart that [he doesn't] have a mandate from the British people."