The Tory Party has made no progress during eight years in opposition and is "deeply defective", leadership contender Sir Malcolm Rifkind has said.
Sir Malcolm says the leadership contest is 'crucial'
The former foreign secretary told the Sunday Telegraph the party's third election defeat was "indefensible".
Sir Malcolm said the leadership battle when Michael Howard steps down this autumn would be crucial.
The party had a choice of continuing down its "cul-de-sac", or choosing an "alternative Conservative tradition."
"The next few months will decide whether we have a future," he said.
Sir Malcolm, who is firmly identified with the left of the Conservative Party, is now MP for Kensington and Chelsea after two terms out of the Commons.
He outlined plans for a consultation on public services which he would launch immediately if he won.
Sir Malcolm, 59, who lost his Edinburgh Pentlands seat in Labour's 1997 landslide, said eight years out of Westminster had given him a unique perspective.
He said: "The last eight years have been deeply, deeply defective.
"There is no excuse that is convincing as to why a party that has been in opposition for eight years should be flat-lining.
"To have seen no increase in the share of the Conservative share of the vote, despite the intense unpopularity of the government, is indefensible."
Sir Malcolm criticised the focus on "classic right-wing Conservative issues" such as immigration, asylum, Europe, crime and tax.
Evidence showed that, with the exception of crime, these were not seen as "gut issues" facing the nation, he said.
"The fundamental strategy of the past eight years has been insensitive to the public mood," he said.