David Cameron is expected to declare that it is his "patriotic duty" to oust Gordon Brown when he speaks at the Conservative's spring conference.
The Tory leader is due to say the party has a duty to win because Britain is in a "complete and utter mess".
He is set to deliver his 40-minute speech without notes as he rallies the party for the general election amid signs their poll lead is narrowing.
The Conservatives have announced their election slogan is "Vote for Change".
The election must be held by June, but it is widely expected to take place on 6 May.
'Broken society'
Recent polls have suggested the Conservative lead over Labour may be narrowing, and Mr Cameron is under pressure to appeal to voters.
In his keynote speech to the conference in Brighton, he is expected to say: "It is an election we have a patriotic duty to win because this country is in a complete and utter mess, and we have to sort it out."
In an article for the News of the World, the Conservative leader says their offer to voters will be based on values of responsibility and aspiration.
Mr Cameron also wrote about Labour's track record and restated his belief in a broken society.
"We'll reform welfare to help more people into work and change the law so that if you're convicted of carrying a knife you can expect to go to jail," he wrote.
The Conservatives have spent their weekend in Brighton attacking Gordon Brown's record.
 George Osborne said Britain could continue down the path of decline |
On Saturday, the party pledged "immediate and real" action in six key areas: dealing with the deficit; boosting enterprise; shoring up families; backing the NHS; raising standards in schools; and cleaning up politics.
In his speech, shadow chancellor George Osborne confirmed a Tory government would hold an emergency budget within 50 days of coming to power, implementing business tax cuts by 2011 to "unleash the forces of enterprise".
He said the country stood at "one of those forks we come across as we travel the roads of our history".
"We can either continue down a path of decline and fall, a path with rising debts, higher interest rates, ever rising taxes and high unemployment.
"Or we can change direction - tell the difficult truths, put debt and taxes back on a downwards trajectory, and create the solid economic foundations of a Britain that works for all. That is the Conservative path."
Labour, whose election slogan is "a future fair for all", have accused the Tories of retreating to the right.
Douglas Alexander, Labour's election co-ordinator, said the Conservatives offered the "wrong kind of change", that people "really can't afford".
The Liberal Democrats say only they offer a change to the existing way of conducting politics.
Danny Alexander, chief of staff to party leader Nick Clegg, said: "It's between the old way of doing politics and the real change represented by the Liberal Democrats".