David Cameron has warned that Britain faces its "hour of reckoning", but insisted the coalition has put the country back on the road to recovery.
The Prime Minister, in a sombre party conference speech, said the UK was back "on the right track" - but warned the challenges ahead were still "daunting".
Speaking just 24 hours after the International Monetary Fund slashed its forecast for UK growth, he declared the choice for Britain was "sink or swim, do or decline".
But drawing on his personal life as the son of a disabled father and the father of a disabled son, he insisted he has the ability and values to turn around the country.
In contrast to Labour leader Ed Miliband and to previous speeches when he has also spoken from memory, Mr Cameron used a script for his address.
It contained no policy announcements and instead focused on his determination to push through the coalition's economic plans to slash the deficit.
"Unless we act, unless we take difficult, painful decisions, unless we show determination and imagination, Britain may not be in the future what it has been in the past," he said.
"Because the truth is this: we are in a global race today and that means an hour of reckoning for countries like ours. Sink or swim. Do or decline.
"To take office at such a moment is a duty and an honour and we will rise to the challenge."
He added: "I know you are asking whether the plan is working and here's the truth: the damage was worse than we thought and it's taking longer than we hoped."
But Mr Cameron insisted: "We are making progress."
He added: "Nothing matters more. Every battle we fight, every plan we make, every decision we take is to achieve that end - Britain on the rise."
He argued that Labour's alternative of borrowing more in the hope of boosting growth would "hurt the economy and hit people hard" by forcing up interest rates.
"We're here because they spent too much and borrowed too much. How can the answer be more spending and more borrowing?" he asked.
Under pressure to make clear to the public exactly what he stands for amid falling poll ratings, he summed up his political beliefs simply.
"There is nothing complicated about me. I believe in working hard, caring for my family and serving my country," he told delegates.
"And there is nothing complicated about what we need today. This is still the greatest country on Earth ... but it's tough. These are difficult times. We are being tested.
"How will we come through it? Again it's not complicated. Hard work. Strong families. Taking responsibility. Serving others."
Seeking to shake off criticism about his privileged background, the Prime Minister described how his father had helped support his own mother when she was deserted by her husband.
His commitment to providing for his family despite his disability meant his life was a "not a hard luck story, but a hard work story", Mr Cameron said.
Amid suggestions about a shift to the right and murmurings of a return to the "nasty party" of old, Mr Cameron insisted he had not abandoned compassionate conservatism.
Conservative policies are "not just good for the strong and the successful, but the best way to help the poor and the weak and the vulnerable", he said.
He derided Mr Miliband's bid to snatch Disraeli's One Nation mantle - calling Labour the party of "one notion: more borrowing".
And he said: "We don't look at the label on the tin; we look at what's in it. We don't preach about one nation, but practise class war. We just get behind people who want to get on in life."
The Prime Minister vowed to support the "doers" in society who are willing to work hard to provide for themselves and their families.
But he insisted plans to reform welfare, support families and back business did not mean the party was giving up on the vulnerable.
"My mission from the day I became leader was, yes, to show the Conservative Party is for everyone: North or South, black or white, straight or gay," he said.
"But above all to show that Conservative methods are not just the way we grow a strong economy, but the way we build a big society.
"That Conservative methods are not just good for the strong and the successful but the best way to help the poor and the weak and the vulnerable.
"Because it's not enough to know our ideas are right. We've got to explain why they are compassionate too."
Shadow Cabinet Office minister Michael Dugher said: "This was a defensive speech, from an out of touch, clearly rattled leader, who cannot be the One Nation Prime Minister we need.
"David Cameron never once mentioned the double dip recession or the one million young people out of work. His speech failed to set out the real change our economy needs."