One of the most striking differences between the United States and Britain is our attitude to religion. The UK is more secular than the US, with views about society, religion and the role of the state nearer to those found in other western European nations and Canada than in the US. The gulf is deep as well as wide. For instance, 60 per cent of Americans believe that the poor are lazy, compared to 26 per cent of Europeans.

Since the end of the Second World War, secularisation has grown in tandem with social modernisation in Europe - a development that some political scientists link to the rise in existential security which accompanied the maturation of welfare states (see Sacred and Secular by Pippa Norris and Ronald Inglehart). A poll conducted for the Economist found that even British Conservatives are more secular than US Democrats. Under 40 per cent of Britons believe that there is a God; yet 80 per cent of Americans do.

The free exercise of religion is given even higher priority than freedom of speech in the first words of the US Bill of Rights, designed in part to free the country from the clutches of the Church of England. This manifests itself in the extraordinary (to a European) proliferation of churches in small US towns, where Catholics jostle with Baptists, Episcopalians, Lutherans, Methodists and orthodox Anglicans.

Blind faith

In a country where eight out of ten people say they belong to a religion and six out of ten pray weekly or more often, it is hard for politicians to be too religious. Despite the official secularisation of the state, US presidents have long sought to derive legitimacy from God, as well as from the people - and not only Republican presidents. John F Kennedy's inaugural address in 1961 ended: "Let us go forth to lead the land we love, asking His blessing and His help, but knowing that, here on earth, God's work must truly be our own." At his inauguration in 2009, Barack Obama spoke of "the knowledge that God calls on us to shape an uncertain destiny".

Bill Clinton memorably used a White House prayer breakfast to apologise for the Monica Lewinsky scandal, declaring that he had sinned and repented: "I ask you to share my prayer that God will search me and know my heart, try me and know my anxious thoughts, see if there is any hurtfulness in me and lead me toward the life everlasting. I ask that God give me a clean heart, let me walk by faith and not sight." Imagine a British politician speaking like that.

On second thoughts, don't - you might invite images of Tony Blair attending baptisms, swathed in white robes. Even in a country as religious as the US, the current line-up of Republican presidential hopefuls is causing some alarm. Mitt Romney and Jon Huntsman are Mormons, Rick Perry and Michele Bachmann are evangelical Christians and Rick Santorum is a conservative Catholic. In August, a profile of Bachmann in the New Yorker that traced her religious influences to a school of evangelical thought called dominionism sparked nervousness among liberals.

Followers of dominionism, in its soft form, believe that Christians should reassert control over political institutions. In its hardest form, it demands the replacement of secular government with Old Testament law. It is derived from Genesis 1:26: "And God said, 'Let them have dominion over the fish of the sea, and over the fowl of the air, and over the cattle, and over all the earth, and over every creeping thing that creepeth upon the earth.'"

One would have thought that there were few alarming religious surprises left in a potential presidential candidate who fasted for three days, asking God whether she should run for Congress; who has advised followers to "be hot for the Lord"; and who once declared: "When we are on fire for Jesus, we can change the world in His name!" Apparently there are.

Some liberals have noted that extreme Christian religions welcome wars and destruction that signal a coming rapture and the return of Christ. When the first reports emerged about Rick Perry's dominionist supporters, Bill Keller in the New York Times demanded that candidates be asked questions about their faith, such as: "Do you agree with those religious leaders who say that the US is a 'Christian nation' or a 'Judaeo-Christian nation'? And what does that mean in practice?" Or, "Would you have any hesitation about appointing a Muslim to the federal bench? What about an atheist?"

Politics of sin

On religious issues, as in politics, US opinion is polarising. Detailed research published in 2010 in American Grace by Robert Putnam and David E Campbell has shown the nation separating into ardent secularists and the highly religious.

The religious generally vote Republican, due to the party's positions on abortion and gay marriage (eight out of ten born-again Christians and two-thirds of white Protestants voted for George W Bush in 2004). The moderates have been squeezed, first by the rise in evangelicalism and now by an increase in secularism, which has occurred as a counter-reaction. In 1973, evangelicals and those with no religion accounted for 30 per cent of the US population; by 2008, the two extremes comprised 41 per cent.

Putnam and Campbell take a largely benevolent view, noting that religious identities are fluid, with roughly 35-40 per cent of Americans switching from their parents' religion at some point, and that interfaith marriage is on the rise. Putnam was raised as an observant Methodist and converted to Judaism on getting married.

To a western European, the shrinking of the moderates is far more alarming. At Tea Party rallies, I have heard the idea of government conflated with sinfulness. It is hard to see how a nation divided between those who think religion has no place in government and those who believe religion demands the destruction of secular government can be governable at all.