LONDON (AP) — Britain ushered in its first coalition government since World War II on Wednesday as a pair of rivals-turned-partners pledged to set aside their deep policy differences and tackle the country’s disastrous budget deficit.

With handshakes, smiles and a sprinkling of jokes, newly minted Conservative Prime Minister David Cameron and his Liberal Democrat deputy Nick Clegg showcased their pact in Downing Street’s sun-dappled garden. “This is what the new politics looks like,” Clegg said.

Cameron and his center-left partner pledged sweeping reforms to Parliament, civil liberties laws and ties to Europe as they made joking reference to the years they spent sniping at each other.

Cameron acknowledged he had once told an interviewer the best joke he had ever heard was “Nick Clegg.”

“Did you really say that?” Clegg said, pretending to walk away from the podium before Cameron comically implored him to come back.

The one-time foes banded together after Britain’s election last week denied all parties a majority — leaving the country with its first hung Parliament since 1974. The Conservatives won the most seats but needed a coalition with the Liberal Democrats to oust the Labour Party after 13 years in office.

Voters struggling during a dismal recession gave no single group a mandate, and many people were left enraged at all politicians after an expense scandal last year in which lawmakers were caught making claims for everything from pornography to chandeliers.

Clegg and Cameron vowed that their partnership would stick so they could deliver the changes voters demanded. They said their pact will hold until Britain’s next national election, and named May 2015 as the date for that vote.

“Until today, we have been rivals. Now we are colleagues,” said Clegg, the surprise upstart of Britain’s election campaign, who won a newly enhanced profile even as his party lost seats.

Clegg will be charged with political reforms, including looking at fixed parliamentary terms. And when Cameron — whose wife is expecting their fourth child soon — is away, Clegg will be in charge, with duties that will include standing in for the weekly and often raucous prime minister’s question time.

Conservatives and Liberal Democrats are divided on many issues, including ties to Europe and election reform, but each side has made some concessions to make the coalition work. The Tories agreed to a public vote on an alternative election system that could benefit the Liberal Democrats, while the Lib Dems agreed it would be several years before Britain even considered closer ties to the European Union.

Cameron and Clegg pledged new fixed-term, five-year Parliaments — replacing a system whereby the prime minister decided on the date; pledged to keep Britain out of the euro currency until 2015 at least; agreed to immediate 6 billion-pound ($8.9 billion) cuts to government waste and vowed that House of Lords members would be elected, rather than appointed.

“It will be an administration united behind three key principles: freedom, fairness and responsibility,” Cameron told reporters in a first joint news conference.

He said the government will immediately begin tackling Britain’s record 153 billion-pound ($236 billion) deficit — and convene a first meeting Wednesday of a newly created national security council, focused on the Afghanistan war. Cameron and Clegg have backed Britain’s current mission but worry about the rising death toll.

Bank of England governor Mervyn King gave a strong endorsement to plans for attacking the deficit, calling it “the single most important problem facing the United Kingdom.”

If the coalition falls apart, it will likely trigger another election.

Although the coalition government says it will put forth legislation to set elections every five years, an election still could be triggered if a motion is brought before the House of Commons. If the coalition were to lose a vote of confidence, another election would have to be called.

One of the first calls of congratulations to the new prime minister came from President Barack Obama, an acknowledgment of Britain’s most important bilateral relationship. Obama invited Cameron to visit Washington this summer.

Both Cameron and Clegg have acknowledged that Labour’s government under ex-leader Tony Blair was too closely tied to Washington’s interests.

The new foreign secretary, William Hague, told the BBC that the new government wanted a “solid but not slavish relationship” with the United States. Hague said the nations won’t agree on everything, but in matters including diplomacy, nuclear issues, intelligence and the Afghan war the U.S. remains “the indispensable partner of this country.”

Hague, a Conservative, is expected to travel to the United States on Friday and will later visit Afghanistan.

Cameron extended his first invitation for formal talks to French President Nicolas Sarkozy, who will visit London on June 18.

The new British leader also spoke Wednesday with two key allies, Chinese Premier Wen Jiabao and Indian Prime Minister Manmohan Singh. He has vowed to build a “new special relationship” with India, believing the country can become a major political and trade partner.

Conservative lawmakers in Cabinet posts include George Osborne as Treasury chief and Theresa May as Home Office secretary.

Aside from Clegg, four other Liberal Democrats have been appointed to Cabinet posts, including Vince Cable, who becomes business secretary. That appointment that may spark nervousness in the financial sector; Cable, an ex-economist for Royal Dutch Shell, is a fierce critic of banking practices and has demanded action to spur lending.

Labour, meanwhile, is entering the unfamiliar role of opposition party. With former Prime Minister Gordon Brown also stepping down as Labour’s leader, former Foreign Minister David Miliband announced his bid to lead the party.

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Associated Press Writers Jill Lawless, Danica Kirka and Sylvia Hui contributed to this report.