Christian campaigners on moral and social issues such as global warming, gay adoption and freedom of expression urgently need to consider their motivations and methods of communications if they are to be taken seriously by secularised Britain, a Christian ethics expert from Cambridge has said.

Dr Jonathan Chaplain was recently appointed director of the Kirby Laing Institute for Christian Ethics in Cambridge. In a speech at the inauguration of the institute, held at the Divinity Faculty of the University of Cambridge, Dr Chaplain said the church was struggling to know how people of Christian faith can most faithfully and effectively represent their political concerns in the context of a liberal democracy.

A democracy, he added, which, on the one hand, has become so "pervasively secularised", and yet, "now houses a ramifying pluralism of voices, both religious and secular".

He said: "The Christian community urgently needs to discern in the pluralism of viewpoints now characterising our society, not only a demanding challenge to its historically inherited public status, but also an opportunity for new avenues of faithful public witness."

Dr Chaplain claimed the current climate in which the church now has to engage was summed up by Prime Minister Tony Blair in a speech last December. Mr Blair said: "Obedience to the rule of law, to democratic decision-making about who governs us, to freedom from violence and discrimination are not optional for British citizens. They are what being British is about. Being British carries rights. It also carries duties. And those duties take clear precedence over any cultural or religious practice".

Dr Chaplain said: "The Prime Minister says 'the obligations of citizenship 'take precedence' over any religious practice'. The Prime Minister was heard to be implying that the political values of the state exercise an unqualified priority over the claims of any religion."

Dr Chaplain told his audience that in his brisk speech, the Prime Minister glossed over the "scope and complexity of the questions he had inadvertently raised".

"But we can be grateful that he raised them, for they lend further momentum to a wide-ranging, far-reaching, and long overdue public debate," said Dr Chaplain.

He said: "The historical roots of representative constitutional government are many and varied, but among the deepest are those deriving from the biblical tradition and the subsequent history of Christian political reflection responding to that tradition. This, in turn, had led to five core principles crystallising Christian thought and experience: principles of equality, freedom, justice, authority, and accountability."

And, he challenged his audience, citing Baroness Thatcher: "A healthy representative democracy needs more than ever, not only conviction politicians, but conviction citizens".

But Dr Chaplain said that if Christians want to make an impact on society and democracy, they need to find a new position and attitude within a pluralistic society, and then communicate more effectively.

He said: "We need a principled pluralism, offering equitable representative status to all political visions seeking to make their voice heard and who are prepared to act constitutionally. This is not only a challenge to Christian people but also a new opportunity.

"It also implies two strategic guidelines: the relinquishing of political privilege, yes, but also the facilitation of confessional candour."

Dr Chaplain says that Christians can no longer assume the right to any privileged status in public debate, as the reality of pluralism is making increasingly untenable the claims of those who seem to favour what has been called a 'Christian nation' stance.

He said: "The Christian nation position invokes the past as a 'norm' for the future: it proposes that Britain's historical Christian formation has created a standing entitlement that Christianity should retain a constitutionally protected influence over culture and law. But this argument falls foul of all such 'traditionalist' arguments: it is never enough to evoke what has been in order to justify what should be.

"Christian political witness today must make its case on a basis of parity with numerous other minority groups. And this should not be a mere reluctant recognition of our minority status, to be quietly abandoned should we acquire majority influence again."

However Dr Chaplain says that Christians must accept their minority status alongside a multitude of contending voices, each one advancing rival and sometimes incompatible political visions, but equally, that "they should remain fearless and unapologetic in contending for their distinctive vision of the public good, insofar as they have one to offer, and they expect others to do the same."

His lecture concluded by saying that "political speech is not preaching", "so I suggest Christians should not enter politics as a platform for evangelistic purposes, but at the same time, representative structures should not try to usher confessionally-motivated political speech to the sidelines in a desire for predictable, accessible, familiar and stabilising public discourse. That would lead to the 'democratic policing' not only of Christianity but of any counter-establishment viewpoint. Democracy should facilitate and not suppress confessional candour." But is it how we communicate Christian values and ideals that Christians most need to address.

He said: "Too often Christians, like many others, are tempted to bypass the time-consuming work of public explanation and fast-forward to a rapid mobilisation of their constituencies on one or other hot-button issue. I recognise, of course, that at times imposed political deadlines seem to leave no other option.

"But of course it's not only Christians who need to heed advice about public explanation: secular-minded believers are also under an obligation to enter into the mindset of religious believers, to ask themselves what might seem reasonable and just from their point of view, given their deepest convictions.

"And because religiously-informed political convictions have been pushed to the margins of public debate for so long, some secular-minded people are finding themselves on a steeper learning curve in this regard than religious believers, who have had to struggle for much longer with how to couch their claims in languages available to others.

"Christians have reasons to remain hopeful about the possibility of political dialogue and to resist retreating into pessimism and balkanisation. But, equitable principled pluralism offers no guarantees of favourable outcomes and it makes for a turbulent ride."