For a president whose policies have polarised America like no other before him, even George W. Bush must have been surprised by the frenzied reaction to his controversial proposals for immigration reform. It is an issue that has ignited intense public passion on all sides, from a civilian 'defence corps' gathering on the US-Mexican border to tens of thousands of immigrant workers marching through American cities to demand greater recognition. Even congressmen fuelled the controversy this month by voting to make English the official language of the United States. The storm over immigration has also highlighted deep divisions within the governing Republican Party, an unwelcome and potentially costly development just six months before crucial mid-term elections. Yet far from quelling the growing unrest, a wide-ranging bill that passed the Senate last week - hailed by some as the most significant and comprehensive overhaul of immigration legislation in two decades - looks certain to add kindling to the fire. The main bone of contention is that it opens a path towards US citizenship for many of the estimated 11 to 12 million immigrants in the country illegally, which critics denounce as an amnesty. This contradicts a parallel bill from the House of Representatives demanding tighter border controls and criminalisation of illegal immigrants, and the two bills must merge before becoming law. 'We have two very separate and distinct directions that we're going in when it comes to controlling our borders and enforcing our laws,' said John Boehner, an Ohio Republican and House majority leader. 'I don't underestimate the difficulties of the House and Senate trying to come together.' Washington observers predict months of wrangling between the factions and say that Mr Bush's bargaining skills will be tested as he attempts to help negotiate a compromise ahead of November elections that could see the Democratic Party seize control of both the House and Senate. 'It's a thorny issue for Bush. He's trying to walk a very fine line,' said James Gimpel, an immigration expert and professor of political science at the University of Maryland. 'But it's not certain to me there will be any dramatic consequence [in the election]. I don't see the Democrats using it against him. If anything, they have an even more permissive stand and can't accuse the Republicans of not being tough enough at the borders.' It is America's porous southern border with Mexico that most concerns the public. Last year, US Border Patrol officers made 1.2 million arrests and estimates that another 500,000 people evaded capture. While all detained Mexicans were returned to their own country, 160,000 others were released in the US due to a lack of space to hold them, and simply disappeared. Agents also found the bodies of 463 would-be immigrants who perished in the brutal desert heat, a 42.5 per cent increase on 2004. Such tragedies have prompted some residents living along the border to leave water bottles out in the desert. The president won praise for explaining his immigration policy in a nationwide television address this month but a sceptical American public will only really judge it a success when it feels the country's borders are secure. Meanwhile, an independent Zogby poll this month determined that 67 per cent of Americans want less immigration, and a CBS poll found that more than 60 per cent supported Mr Bush's decision to send 6,000 National Guard troops to help enforce the Mexican border. Much of the outcry, however, has been over those who have already entered the US illegally and are now working in mainly low-paid, manual labour or agricultural jobs, generally in Texas, California, Florida and New York. Some argue their presence is a burden on overstretched social services, including health care, housing and welfare benefits. Others say they fill the jobs Americans are unwilling to do, and are crucial to the smooth running of the country and its economy. Either way, they make up almost 5 per cent of the workforce, and include at least 6.2 million from Mexico and 2.5 million from Cuba and other Latin American countries, according to the Pew Hispanic Centre. These migrants and their supporters have long demanded formal recognition and stepped up their campaign this month with a one-day work stoppage. Their calls were echoed last week when Vicente Fox, the Mexican president, made a high-profile four-day visit to the US and called for a bilateral solution. 'Mexico believes that it will take more than just enforcement, building walls, to really solve the challenge posed by the migration phenomenon,' Mr Fox said in Seattle, responding to congressional plans to build a 1,120km fence along sections of the 3,200km land border with his country. As a compromise, the Senate agreed to consult Mexico before construction began. The Senate plan would allow undocumented workers who have been in the US for more than five years to obtain citizenship by learning English and paying taxes and fines, and require those there between two and five years to return to an entry point to apply for the guest-worker programme. Critics have denounced the plan as an approval of criminal enterprise, given that many of the migrants have claimed social security benefits with forged or stolen documents. 'Does this bill punish the people who stole an American citizen's identity? No, it does not. It rewards them,' said John Ensign, a Republican senator from Nevada. But Arizona's Senator John McCain, a fellow Republican and co-author of the Senate bill with Democrat Edward Kennedy, disputes this. 'This is in no way an amnesty,' he said. 'When Americans understand the problem, they think that earning citizenship is the way to go. And I emphasise earning ... paying back-taxes, passing a background check, waiting for a green card. You can't just round up 11 million people and send them back.' For the Minutemen, organised groups of self-styled patriots and citizen activists who have taken to patrolling the Mexican border to observe and report illegal immigrants, Senator McCain's views cut little ice. Fed up with what they see as the government's unwillingness to take action, teams of volunteers will tomorrow break ground on their own high security border fence on private land in Arizona. 'We will continue our efforts to make sure America's borders are secured with all speed,' said Chris Simcox, president of the Minutemen Civil Defence Corps.