The American invasion of British politics has been a long war of attrition. Each successive campaign since the 1990s has increasingly taken on the flavor of U.S. electioneering: first came war rooms and rebuttal teams, then voter targeting, personal attack ads and, in 2010, the first televised debates.

Now the invasion has become a full-on assault, with former Obama staffers David Axelrod and Jim Messina signing up as political consultants on opposite sides in the coming election that will determine the next prime minister.

Messina, who is working with the Conservative Party and Prime Minister David Cameron, served as the White House deputy chief of staff and ran President Obama’s reelection campaign.

Axelrod, who is assisting the opposition Labor Party and its leader, Ed Miliband, has been a longtime Obama confidant and speechwriter, and worked in the White House as senior adviser.

Thanks to the influence of Messina and Axelrod, the increasing role of online campaigning and new laws that clear the way for a longer election, politicos in Britain think the campaign for the election in May will mark a tipping point in the strategic use of voter data, TV and social media.

In this Feb. 10, 2009, file photo, then White House Senior Adviser David Axelrod, left, and then White House Deputy Chief of Staff Jim Messina walk to board Marine One at the White House in Washington. (Ron Edmonds/AP)

“I think 2015 will see the boundaries being pushed with ads online, through YouTube, Spotify and on-demand television,” said Matthew Elliott, a conservative campaigner behind two American-style pressure groups in London, the TaxPayers’ Alliance and Business for Britain.

“In the U.K., parties have a much better command of the media, and the looser regulation of online ads could be a game-changer,” he said.

At present, Messina’s influence on the campaign is more pronounced than Axelrod’s. He has been closely engaged in strategic planning with the Conservative Party since chairman Andrew Feldman and chief strategist Lynton Crosby hired him in August 2013. He has been visiting Britain for a handful of days every month and speaks to Conservative headquarters daily.

Just as he did for Obama, “the Fixer” has been focused on improving the party’s social media output and beefing up its ground operation and fieldwork. His expertise in breaking down and analyzing granular groups of voters may also prove useful for a party that is attempting to build a broad coalition to remain in power.

In an interview, Messina said he is “very proud to be part of the team” and cites the prime minister’s “unparalleled” record in office as his motivation to take the job.

The admiration is mutual — during the annual Carlton Political Dinner, the major fundraising dinner for the Conservatives before the election, Feldman described Messina as “the best center-left campaigner in the world for targeting voters” and received a round of applause.

Like Messina, Axelrod is being paid handsomely by British standards — reportedly about $500,000. But he offers his input mostly from his desk in Chicago. He has visited the party’s headquarters in London once, and he has participated in weekly conference calls and chimed in on strategic e-mail threads.

That might change. Traditionally, British elections have focused on policy and party. But personalities have become increasingly important — and Axelrod’s specialty is crafting a candidate’s persona. During his six years advising Obama, Axelrod used the president’s biography as his most effective campaign tool.

“David Cameron wants to make the next election not about parties, but ‘who do you want to be prime minister,’ because he has a huge polling lead over Ed Miliband on that question,” says Peter Kellner, president of the British polling company YouGov.

“Although his team may be pushing hard with this approach, it won’t work quite as well as in the United States, because Cameron and Miliband’s names won’t be on the ballots, unless you live in their individual constituencies,” he said. “Because of this, British elections are still much more about local candidates.”

Axelrod is also a master at messaging. Though his fingerprints could be seen on Miliband’s conference speech this year — one of the key passages stressed his opposition to “you’re on your own” policies, something Obama did when launching his reelection bid — Axelrod said he was not “deeply involved” in writing the speech.

Hinting at the future work he might do for Labor, Axelrod said in an interview that targeting voters via extensive polling and focus groups, something he helped pioneer in Obama’s campaigns, will be important.

“In the U.S., all 50 states are involved in the election, but eight, 10, 12 become absolutely pivotal in the outcome,” he said. “The same will be true in the British election. The ability to target with some precision is really important.”

Some in the Labor Party, however, are concerned that Axelrod’s style of consulting from a distance, not uncommon in the United States, has its limits and are anxious for him to decide whether he is fully committed.

“You cannot spend 300,000 pounds on a press release. Axelrod can no longer just cash the checks and send e-mails. You need boots on the ground,” said a Labor strategist who spoke on the condition of anonymity because he was not authorized to talk to the news media on behalf of the party. “After all, he doesn’t want to lose to Jim Messina, does he?”

Axelrod said that he is open to the idea of becoming more involved with Labor after his memoirs are released next year but that “we haven’t had that discussion.”

Although Messina and Axelrod are lifelong Democrats, many in Washington were surprised when they signed up for parties on opposite sides in Britain, adding a personal rivalry to the 2015 campaign.

“I’ve known David Axelrod for many years, and I’m sure he’s outraged at the idea of Jim Messina working for the Conservative Party,” said Stan Greenberg, a Democratic pollster who has worked with the Labor Party since the 1990s.

Axelrod denies there is a conflict and says he does not view the next British election as “a personal matter between Jim and me.”

“Jim’s a friend,” he said. “We’ve worked together for years. He is a skilled professional, and I’m sure he’s getting paid very well over there for doing what he’s doing, and I’m sure he’s bringing value to their effort.”

Messina also stressed that there is no personal rivalry. “David is my brother and I love him,” he said. But Axelrod has noted it has been some months since they have spoken. “I think he’s just so busy he’s lost track of how long it’s been,” Axelrod said.

Though Axelrod and Messina are taking British politics to a new level of Americanness, there’s still a long way to go in at least one category — the amount of money spent. During the 2010 election, the total spending by all the parties in Britain was nearly $50 million, according to the Electoral Commission in London. In the 2012 U.S. presidential election, the Center for Responsive Politics estimates spending at $7 billion.