I couldn’t believe it. I was trying to discuss traditional marriage – and the state was trying to stop me.

Incredible, in a 21st-century European country, but true. I was invited to speak at a conference on marriage last summer, to be held at the Law Society in London. The government had just launched a public consultation on changing the law to allow same-sex marriage. The conference was a chance for supporters of traditional marriage to contribute to the debate. The participants included a retired philosophy professor, a representative of the Catholic archdiocese of Westminster, the chairman of the Tory party’s oldest pressure group, the Bow Group, Phillip Blond (another Tory adviser) and spokesmen for various Christian organisations. The title, “One Man. One Woman. Making the Case for Marriage for the Good of Society”, could hardly have sounded more sober. I accepted without a second thought.

A few days before the conference, someone from Christian Concern, the group which had organised the event, rang me in a panic: the Law Society had refused to let us meet on their premises. The theme was “contrary to our diversity policy”, the society explained in an email to the organisers, “espousing as it does an ethos which is opposed to same-sex marriage”. In other words, the Law Society regarded support for heterosexual union, still the only legal form of marriage in Britain, as discriminatory.

Hurriedly, another venue was found, the Queen Elizabeth II Conference Centre in the heart of London. This publicly owned modern building is named after the supreme governor of the Established Church, and is situated across the street from Westminster Abbey, for nearly a millennium the symbol of Christian Britain. Who could hope for a better venue, in short, to discuss what the churches still regard as a sacramental union?

But with only 24 hours to go before the conference, managers at the QEII centre told Christian Concern that the subject it planned to discuss was “inappropriate”. The booking was cancelled. When challenged, the QEII centre’s chief executive, Ernest Vincent, cited its diversity policy as reason for the cancellation. A journalist asked for a copy of the diversity policy. The centre refused to provide it.

By the time I took part in the event, (which had been moved to the basement of a hotel in central London), I felt my rights as a taxpayer, citizen and Christian had been trampled. I began to wonder if I had been the unlucky victim of an isolated incident or was in fact encountering a wider problem. I started to research the issue.

My findings were shocking: not only Christians, but also Muslims and Jews, increasingly feel they are no longer free to express any belief, no matter how deeply felt, that runs counter to the prevailing fashions for superficial “tolerance” and “equality” (terms which no longer bear their dictionary meaning but are part of a political jargon in which only certain views, and certain groups, count as legitimate).

Only 50 years ago, liberals supported “alternative culture”; they manned the barricades in protest against the establishment position on war, race and feminism. Today, liberals abhor any alternative to their credo. No one should offer an opinion that runs against the grain on issues that liberals consider “set in stone”, such as sexuality or the sanctity of life.

Intolerance is no longer the prerogative of overt racists and other bigots – it is state-sanctioned. It is no longer the case that the authorities are impartial on matters of belief, and will intervene to protect the interests and heritage of the weak. When it comes to crushing the rights of those who dissent from the new orthodoxy, politicians and bureaucrats alike are in the forefront of the attacks, not the defence.

I believe that religious liberty is mean­ingless if religious subcultures do not have the right to practise and preach according to their beliefs. These views – for example, on abortion, adoption, divorce, marriage, promiscuity and euthanasia – may be unfashionable. They certainly will strike many liberal-minded outsiders as harsh, impractical, outmoded, and irrelevant.

But that is not the point. Adherents of these beliefs should not face life-ruining disadvantages. They should not have to close their businesses, as happened to the Christian couple who said only married heterosexual couples could stay at their bed and breakfast. They should not lose their jobs, which was the case of the registrar who refused to marry gays. When Britain was fighting for its life in the Second World War, it never forced pacifists to bear arms. So why force the closure of a Catholic adoption agency that for almost 150 years has placed some of society’s most vulnerable children with loving parents?

Once a dominant force in western culture, religion has been demoted to, at best, an irrelevance; at worst, an offence against the prevailing establishment. For millennia, religion has coloured every aspect of the European landscape. Churches were every­where – one for every 200 inhabitants in the High Middle Ages – and oversaw every stage of life: “hatch, match and despatch”. Philanthropists, religious orders and communities built and ran schools, orphanages and hospitals. Belief was so crucial to ordinary people that the most destitute did not question paying tithes to their church. The Founding Fathers crossed an ocean to be free to practise their faith.

But, as the British poet Geoffrey Hill has written, the continent is “a place full of memorials but no memory”. Church attendance has slumped to less than 30 per cent. Only in two Greek Orthodox countries, Cyprus and Greece, does the overwhelming majority of the population attend services regularly (98 per cent and 96 per cent respectively). Europeans may walk in the shadow of church spires but biblical literacy is so unusual today that a recent survey found that, of 900 representative respondents, 60 per cent couldn’t name anything about the parable of the Good Samaritan, while only 5 per cent of people could name all the Ten Commandments.

Americans do God in a way that Europeans no longer do: the First Amendment guarantees citizens’ right to the “free exercise of religion” – and they in turn choose to exercise their religion in a host of patriotic rituals. Their currency (“In God we trust”, proclaims the dollar bill), the prayer before the college football game and the national anthem: all invoke God, and pledge faith in His powers. “All-American” is synonymous with church-going, just as “un-American” meant the Godless communists.

The equation – good equals God-fearing, and bad equals atheist – is so much part of the ordinary mindset that when asked in a recent study whether a fictional hit-and-run driver was more likely to be a rapist or an atheist, most Americans chose an atheist. It seems preposterous, given this scenario, to speak of an encroaching atheism. Yet stealthily, behind an advance guard of political correctness, a new secularism is taking shape. As in Europe, it elevates gay rights, women’s rights and pro-choice principles to unassailable values. To question them is to court censure and worse.

Can the decline in the social and intellectual standing of faith be checked, or even reversed? Yes. Ironically, believers can learn from those who have come to see themselves as their biggest enemy: gays.

Think of how successful gay rights activists have been, in both Europe and America. Twenty-five years ago, Britain’s first “gay pride” march took place in London. It was a muted affair, remembers the campaigner Ivan Massow, which “struggled to fill half of Kennington Park and a disco tent”. Today, the Gay Pride march is sponsored by the Mayor of London and draws tens of thousands, filling Hyde Park. Prime Minister David Cameron was on hand last summer to take credit for equal marriage reforms which would allow gay schoolchildren to “stand a little bit taller”. The Royal Bank of Scotland was in evidence to take credit for sponsoring high-profile gay awards. Everyone, it seemed, wanted to be in on the act.

Practising Christians, Jews and Muslims should also step forward into the limelight, dismantling prejudices that they must be suspect, lonely, losers. Believers should present themselves as ordinary people, men and women who worry about the price of the weekly shop and the size of the monthly mortgage. They should not appear to be religious zealots or gay-bashers or rabid pro-lifers. They should reassure critics that religious people are not a race apart – but just happen to cherish a set of ideals that sometimes places them at odds with the rest.

Let outsiders see the faithful as a vulnerable group persecuted by right-on and politically correct fanatics who don’t believe in free speech. Let them see believers pushed to the margins of society, in need of protection to survive. Banned, misrepresented, excluded – and all because of their religion? Even the most hardbitten secularist and the most intolerant liberal should be offended by the kind of censorship people of faith are facing today. If believers can awaken a sense of justice in those around them, they may have taken a first important step in reclaiming the west as an area where God is welcome.

Without a change, the work that faith groups have carried out for millennia – charities, hospitals, schools, orphanages – will disappear. Communities will no longer be able to rely on the selfless devotion of evangelists and missionaries who happily shoulder the burden of looking after the unwanted, the aged, the poor. Feeling stigmatised and persecuted by the authorities and the establishment, Christians, Muslims and Jews may well become entrenched in the more fundamental shores of their faith.

Equality is already becoming the one civic virtue universally endorsed; equality legislation, the overriding principle of law. In this new scenario, yesterday’s victims are today’s victors. Gays and women, among other scapegoats from the past, now triumph over their former persecutors. But they have learned no lesson from their plight. As they promote a one-sided tolerance, they act as if their rights now include this: to have no one disagree with them.

This is not the sign of a healthy society. Ordinary citizens should not live in fear of saying or doing “the wrong thing”. Diversity means respecting conscientious objections and making reasonable accommodation to let subcultures survive. Erasing God from the public square, and turning religion into a secret activity between two consenting adults in the privacy of their home, leads to what the poet Seamus Heaney calls the hollowing-out of culture. A no-God area can only sustain a fragile and brittle civilisation, a setting worthy of a broken people.

The roots of today’s intolerance, however, run deep. Decades of totalitarian regimes instilled suspicion of authority; while the birth of ethical relativism taught that everything goes – just not judging others. Religion took no account of these historical developments. It was authoritarian, judgemental, and hypocritical to boot. The Ayatollah Khomeini’s fatwa against Salman Rushdie and the terrorist attacks on 11 September 2001 showed Islam was guilty certainly of the first two accusations; the abysmal cover-up by the Catholic Church of its priests’ paedophile abuse exposed it as guilty of the third.

Given the precedents of the past century, westerners today should be hard-wired to resist the persecution of religious people. Of course, it would be blasphemous to compare the hardships of Christians, Muslims and Jews in the west today to the plight of their forebears in totalitarian regimes or to their co-religionists elsewhere, who live in fear for their lives and are being systematically abused and driven from their homes. To be a Christian in Iraq, Egypt or Pakistan, or a Muslim Uighur in Xinjiang, western China, or a Buddhist in occupied Tibet, means routine persecution. A law suit, a disciplinary hearing at work, or even hate speech online or in person can seem insignificant by comparison. But that is no reason not to mind.

Religion has long been synonymous with authority. This was no bad thing when, for millennia, traditional hierarchies were respected for ensuring that the few at the top protected, organised, and even ensured the livelihood of, the many at the bottom. Bloodthirsty authoritarians from Hitler to Pol Pot drove a tank through this vision: they turned authority into authoritarianism. Those who survived their brutal regimes and those who witnessed them cherished their individual liberty, once they regained it, all the more.

Personal choice became a new morality. Those institutions that stood in its way –the class system, the army, the Church – sparked fierce hostility. Hippies, rock stars, comedians, university students and their professors, draft evaders and military deserters took up arms against the old order. Christians, too, cheered the triumph of liberty but they held back when “liberty” bred the celebration of the “I”. Christian churches, especially the Roman Catholic, insisted that individuals were not free to do as they wished, but bound by divine laws to obey an invisible God. Birth, marriage, speech, sexuality: the Church had rules and regulations for every area of everyday life.

By the 1960s Vatican insiders felt they must modernise their ancient world to retain some of its inhabitants. Vatican II (1962-65) allowed Pope John XXIII, the pontiff said, to throw open the windows of the Church to let in some fresh air.

But while he allowed for the translation of Latin prayers and said priests could face their congregation during Mass, his encyclical Humanae Vitae quashed talk of a new sexual ethics. Self-denial remained a core message. The Church would continue to oppose divorce, homosexuality and the Pill as grievous sins.

The Church saw itself as a rock in the shifting sands of public mores; critics saw it as implacable and unbending – and let the world know what they thought. “Catholic baiting is the anti-Semitism of the liberals,” the priest and author Andrew Greeley wrote then. These critics drew their own inspiration from a Harvard professor. Joseph Fletcher’s Situation Ethics, published in 1966, argued for a new morality where nothing was universally right or wrong; context, or situation, was everything. Truth itself became subjective – or truth-for-me, as Fletcher’s critics dubbed it.

Fletcher’s tabula rasa was exciting. It ushered in a “permissive society” whose members felt thoroughly emancipated from Judaeo-Christian ethics. In this way, secularism became allied to a newfangled “liberalism”. Yet even its staunchest opponents could not completely reject the Church. In occupied countries such as Poland and Ireland, the Catholic Church had supported the underground opposition against the occupying regime and won, in the process, every patriot’s heart.

In 1989, however, Ayatollah Khomeini declared a fatwa against Salman Rushdie for his “blasphemous” novel The Satanic Verses. The world recoiled at the extraordinary curse from an exotic corner of the world. Then, in quick succession, Rushdie had to go into hiding; his Japanese translator was killed; and his Italian and Norwegian publishers were knifed. The west understood a terrifying new force had been unleashed: here, in black cloaks and long beards, stood the enemies of free speech.

It didn’t matter that a long list of leading Muslim writers rushed to declare their support for Rushdie and free speech. For the liberal intelligentsia, the Rushdie affair marked a turning point. They were witnessing one of their own persecuted by a sinister authoritarian regime that, in God’s name, opposed everything they believed in. To tolerate this faith was to repudiate hard-won rights of free speech and, above all, equality.

Atheists seized their chance: shrewdly, they pointed to the ayatollah’s quashing of free expression as representative of a religious mindset: blasphemy laws were part of the Judaeo-Christian legacy, too. They went on to elide Islamism with all religions; Muslim practices mirrored Christian and Jewish tenets, Islam was just another attempt to deal with the great fairy in the sky.

The 11 September 2001 attacks gave the secularist campaign to discredit religion a whole new impetus. The tragedy reawakened fears of Islam. The commentary surrounding the 19 terrorists wove elements of fanaticism and A Thousand and One Nights into the inspiration for these gruesome acts. In fact, most of the hijackers and their accomplices could not be considered model Muslims; they were alcohol-swigging middle-class youngsters who had hung out in Las Vegas (some with prostitutes there).

Muslim leaders around the world should have stood as one to condemn the acts of terrorism and distance themselves from the fanatical spirit that had sparked them. More recently, the leaders of the Catholic Church (and to a lesser extent the Anglican one) also failed to condemn the horrific crimes committed by co-religionists. The horror of paedophilia among priests was magnified by the Church’s attempt to cover up the scandal. The hierarchy’s reluctance to expose and punish their clergy discredited the institution – among its faithful as well as its foes.

For some new foes, such as the late Christopher Hitchens and Richard Dawkins, the Church was not accommodating child abuse, it was child abuse. As Dawkins told an audience in Dublin, “horrible as sexual abuse no doubt was, the damage was arguably less than the long-term psychological damage inflicted by bringing the child up as Catholic in the first place”.

Dawkins hailed the words of a psychologist, Nicholas Humphrey: “Children have a human right not to have their minds crippled by exposure to other people’s bad ideas.” Humphrey, like Dawkins and Hitchens, caricatured religion as superstition and dogma, and its followers as stupid. The new atheists, mainly scientists and authors, saw themselves as truth-seekers. They touted their own false equation without pause – science and religion are locked in inevitable and perennial conflict. They rewrote history to present the Enlightenment as a battle between two mortal enemies: reason v religion.

The faithful, according to this manipulation of history, stood on the side of obscurantism and ignorance. Believers turned their back on progress, rejected Darwin and hated women. Ranged against them were the forces of good – the new atheists, who shed light on the dark and sinister workings of religions.

With these clever and rational men (they were all men) as guides, ordinary folk would find their way to the sunny plateaus of a rational existence. Here men and women, emancipated from the old superstitions, would breathe the pure oxygen of equality and learn that nothing lurked beyond matter. “Transcendence”, “spirituality” and “salvation”: atheists would expose these concepts as empty talk, with no bearing on real life.

In this way the stage was set for a new intolerant agenda.

Cristina Odone’s ebook “No God Zone” is out now (Kindle Single, 99p)

Now read a response to this piece by the comedian and secularist campaigner Robin Ince

Correction: this article referred to the fatwa on Salman Rushie occurring in 1979. It has been amended to 1989.