The frank warning was delivered to around 1,000 Evangelical Christians at the Bible by the Beach conference held in Eastbourne over the weekend.
They heard how equality laws have led to the dismissal of Christians who offered to pray for clients or patients, the closure of adoption agencies that refuse to place children with same-sex couples, and charities losing funding because of their Christian ethos.
The conference explored the court ruling last week involving Gary McFarlane, a relationship counsellor with Relate Avon who was dismissed for telling his employers that he could not counsel same-sex couples because of his Christian beliefs.
He lost his legal bid to bring his dismissal before the Court of Appeal after Lord Justice Laws ruled that the Christian faith was "subjective" and "incommunicable by any kind of proof or evidence", and that it would be "divisive, capricious and arbitrary" to protect a moral position held on purely religious grounds.
The Bishop of Lewes, the Rt Rev Wallace Benn, argued that the Church of England was still the established Church and one of the UK's three constitutional guarantors of civil freedoms, alongside Parliament and the monarchy.
He warned that Christians needed to be aware that "rampant, illiberal secularism" had become the prevailing attitude in the UK.
"We need to understand what's going on at this moment in time. We are at a very, very tricky point as a nation because there is not a consensus commitment to anything else except hardline illiberal secularism and it's a very dangerous place to be," he said.
"We need to know what our heritage is, encourage people to return to it, and encourage Christians to be informed and stand up and be counted – graciously, but clearly and firmly."
The conference was joined by Mike Ovey, Principal of Oak Hill Theological College, who said he had been "shocked" by the "intellectual incoherence" and "godlessness" of Lord Laws' judgement.
He said: "If one of my students in their first year had written that I would have failed them ... Why? Because the Christian faith is not just subjective but it is rationally communicable."
He asked the audience: "Do you believe? Did someone transmit and explain the faith to you? Yes. So to say that [the Christian faith] is just subjective is simply not true. Somebody made you believe.
"Lord Laws also believes something, he fails to see that he has a faith too ... secularism fails to understand that it is a religion."
He went on to say that Christianity was not only being marginalised in the UK but that there was a "deeply held antipathy" to the Christian faith and that other faiths were being treated more fairly than Christianity.
Alistair Begg, senior pastor at Parkside Church near Cleveland, Ohio, quipped: "Climate change is a protected belief in our society but Christianity is not."
Andrea Williams, director of the Christian Legal Centre and Christian Concern For Our Nation, said the law was "against" Christians in the workplace and that even where Christians had won their unfair dismissal claims, they had faced hostility from staff on their return to work.
"The law is being used to oppress," she said. "Judges don't understand that for a Christian, being free doesn't simply mean being free to think like a Christian. It means that when a Christian goes to work they need to act like a Christian and work like a Christian."
She continued: "We are certainly seeing the marginalisation of Christianity. In a biblical interpretation, it could be persecution, not like our brothers and sisters losing their lives in other countries, but the next step is criminalisation.
"It's time to say 'not on my watch' and in love and grace, speak the truth to a broken and heartbroken society."
The wide-ranging panel discussion also touched on issues of church unity and communicating controversial aspects of the Christian faith, like the concept of hell.
Begg said that although it was easy to look at the early church as if it were always at peace, there were in fact quarrels and disagreements.
He said it was not a "cop-out" for Christians to say they were united in Christ.
"It may not always look like it, but we are united," he said.
He added that Christians had to be realistic about their faults and heed Paul's words to "bear with each other".
"I don't have to like Wallace Benn, I just have to love him," he joked.
He warned pastors in particular that if they could not lead in this aspect, then their congregations would simply follow their example.
"We can have various views but we must love each other sincerely in Christ," he said.
Bishop Benn said Christians needed to stop going into relationships expecting the worst of other Christians.
He said: "We need to give each other the benefit of the doubt positively. Too many Christians give the benefit of the doubt negatively."
Williams, meanwhile, urged the church to proclaim the truth, arguing that its voice had become "muffled and mute" in society because pastors had stopped speaking out on difficult issues from the pulpit.
"Hell is simply the truth being known too late," she said. "Politics is not the answer. Jesus is the answer. I pray that we will find our voice. What compels us to speak the Gospel is believing in hell and the fact that we don't want anyone to go there."