Addressing media outside the official prime ministerial residence at 10 Downing St., Cameron said that Britain had been "on the brink" when he came into office. "Of course, we haven't fixed everything, but Britain is back on her feet again."
Cameron said the nation faced "a stark choice" in 38 days. "The next Prime Minister walking through that door will be me or (Labour Party leader) Ed Miliband," he said.
"You can choose an economy that grows, that creates jobs, that generates the money to ensure a properly funded and improving NHS (National Health Service) ... and a government that will cut taxes for 30 million hard-working people ... or you can choose the economic chaos of Ed Miliband's Britain," Cameron said.
"After five years of effort and sacrifice, Britain is on the right track. This election is about moving forward -- and as Prime Minister here at No. 10 that's what I will deliver."
Labour: 'Clear and present danger'
Miliband launched Labour's Business Manifesto on Monday, saying that a second Conservative term would threaten Britain's EU membership and pose "a clear and present danger"
to British firms and prosperity.
"There are two futures on offer at this election," Miliband said. "To carry on with a Conservative plan based on the idea that as long as the richest and most powerful succeed, everyone else will be OK. Or a Labour plan, a better plan, that says it is only when working people succeed that Britain succeeds."
Miliband also referenced Cameron's March 23 announcement that the Conservative leader had ruled out standing for a third term -- before the election that will decide whether he even gets a second term in the top job -- saying the Conservative candidates would be "vying against each other for who can be the most extreme on Europe."
Cameron and his Conservative Party won the last election in 2010, but not by enough to go into government alone.
Without a majority in Parliament, a government becomes dependent on MPs, or lawmakers, from other parties to get its program voted through the House of Commons, the chamber that passes laws and legislation.
For five years, Cameron has been governing in coalition with the UK's third party, the Liberal Democrats.
Nick Clegg, Liberal Democrat leader and deputy prime minister, has mostly backed Cameron in parliamentary debates against Labour's Miliband.
"For the first time ever, the Liberal Democrats go into this campaign with a record of action in government to be extremely proud of," Clegg said Monday.
"We have kept the government in the center ground and shown that we are the only party that can build a stronger economy and a fairer society."
The right-wing UK Independence Party, or UKIP, which has pledged to take the UK out of the European Union, has made massive gains in the past year -- mostly at the expense of Cameron's Conservatives.
Last year, in a backlash against the EU, UKIP caused a political earthquake and won elections to the European Parliament in Britain, and some commentators have likened its impact on UK politics to that of the tea party in the United States.
UK 'tea party'
It is unclear how UKIP will perform in the May 7 UK general election. Some of its supporters appeared to be casting protest votes last year and could return to the established Conservative and Labour parties when more is at stake.
On Monday, UKIP leader Nigel Farage tweeted: "UKIP is the party of real change for real people. If you #VoteUKIP on May 7th, you'll get MPs willing to hold the government to account."
Meanwhile, in Scotland, the September independence referendum (which narrowly failed) so reinvigorated the Scottish National Party that it could hit what is usually a key Labour stronghold, undermining Miliband's bid for power.
Scottish National Party leader Alex Salmond quit after the referendum, and Nicola Sturgeon now heads the party.
"The general election on May 7 is a fantastic opportunity for Scotland to make Westminster sit up and take notice," Sturgeon said Monday.
"By holding the balance of power in a hung Parliament, SNP MPs can work with others to lock David Cameron out of Downing Street -- and ensure that Scotland's priorities become priorities at Westminster," she said.
Eligible Britons must be registered by April 20 to vote.