David Davis has said the Conservatives must offer a "starkly different alternative" to Labour rather than trying to be the "heir to Blair".
Davis: "Can understand the issues"
Speaking at his old south London school, the 56-year-old argued for a "distinctive low-tax agenda for growth" and "real choice" in public services.
The shadow home secretary's comments will be seen as a dig at his rival for the Tory leadership, David Cameron, 39.
Mr Cameron's youth and style have led some to call him "Tory Blair".
Visiting a community IT project at Ernest Bevin School, formerly Tooting Bec Grammar School, Mr Davis said the Conservatives could not win the next election by "continuing with a Blair settlement".
Mr Davis said "real change" was needed to create a true "opportunity society".
"What I don't believe in is being an heir to Blair, accepting the Blair settlement," he said.
"Blair won against a Tory government coming to the end of its life and probably would have won whatever he had done."
State-educated, unlike Old Etonian Mr Cameron, Mr Davis said the Conservatives needed to win in cities, adding: "I understand the sorts of issues these youngsters feel."
Mr Cameron, shadow education secretary, is the bookmakers' favourite, having won the final vote by MPs last week.
His list of supporters outside parliament was swelled on Tuesday by the addition of Middlesbrough Mayor Ray Mallon - the former Cleveland Police officer dubbed Robocop for his zero-tolerance approach to policing.
Despite being elected as an Independent, Mr Mallon said he liked Mr Cameron's "leadership" qualities and his ideas on fighting crime.
"We see a guy who knows where he's going and who's got the character and the charisma to take people with him," he said.
Ballot papers for the 300,000 Tory members who will decide the contest are being sent out next week.
Hustings, where the candidates appear head to head, will be held around the country before polls close on 5 December
The results will be announced the following day.