Headlines screaming of the need to up arms and defend our 'Christian culture' have become a bit of a cliché in recent months, particularly as Islamist extremists dominate the news.

On Monday, UKIP leader Nigel Farage – who has been criticised for trying to score political points in the wake of tragedy – used last week's Paris killings to demand that we step up our resistance to those trying to undermine our societal values.

"We do have, I'm afraid, I'm sad to say, a fifth column that is living within our own countries, that is utterly opposed to our values," he said before a European Parliament debate.

"We've been guilty of weakness, of lack of courage, of lack of assertion in who we are as people...We're going to have to be a lot braver and a lot more courageous in standing up for our Judeo-Christian culture."

Farage's comments follow a series of debates last year after government minister Eric Pickles condemned "militant atheists", saying: "We're a Christian nation...Get over it".

David Cameron then insisted that Britain should be "more confident about our status as a Christian country" and politicians far and wide fell over themselves to praise our religious heritage.

It's a mantle that has been taken up perhaps most loudly, however, by the Far Right – as demonstrated by Farage, and indeed Britain First, an offshoot of the BNP. Its leader, Paul Golding, recently told Christian Today that in moving away from inbuilt Christian values, "our entire moral, cultural and religious fabric is falling away, and making us a much weaker and more degenerate country."

But what exactly is a Judeo-Christian culture, and why are so many people who don't subscribe to either religion so keen on defending it?

Christianity is no doubt entrenched in British history. Our holidays, flags and national anthem all speak of a country built on the Christian faith. Our language is saturated with biblically-linked idioms, even the seven day week has its roots in Judaism and the story of Creation.

"The link between Britain and Christianity has been firmly established since King Athelbert was converted to Christianity by Augustine in 597. That was over 1400 years ago, [and] over that time Christianity has firmly cemented itself into our national culture, structures and subconscious," explains Gillan Scott, founder of God and Politics in the UK and deputy editor of the Archbishop Cranmer blog.

"Much of our lives are infused with Christian principles and heritage irrespective of our individual beliefs. The thing is that it is so ingrained in our national identity that much of it is taken for granted – Christian values and morals make up our Britishness far more than most of us realise. Even Humanism derives much of its morality from Christianity, whether its proponents choose to acknowledge it or not."

Chief Executive of CARE, Nola Leach, told Christian Today that the UK has "unquestionably" benefited from a rich Christian heritage and values which are embedded in every corner of our society.

"These very values are of tremendous benefit, not just for some but for everyone because they reflect the will of God for human flourishing," she says. "So the desire to see Christian values upheld is above all a desire to see good for all people, wherever they come from."

But historically Judaeo-Christian though it may be, does Britain remain so? Are we slipping into a secular abyss, or being consumed by other religions as the melting pot grows ever more diverse? 

"As a society, not as individuals, we've rubbished the whole idea of God, and we've secularised public life," Alan Craig, formerly the leader of the Christian People's Alliance and now a UKIP supporter, told Christian Today.

"We've turned ourselves aggressively against God publicly... Lots of things contribute to culture, but the Christian religion has been foundational to Britain. It forms the very nature of our society."

It's important to recognise our history. It helps prevent us from repeating past mistakes, and shapes our future. But there's no denying that while once the majority of Brits were Christians, fewer and fewer of us now identify with the faith. 33.2 million said they were Christian in the 2011 census, a decrease of 4.1 million in ten years, while the Muslim population increased by 1.2 million in the same time period. The number of people who reported they had no religion at all saw an even larger increase of 6.4 million.

However Christians on the Left director Andy Flannagan does not see this an either/or situation. "A diverse, welcoming culture is a Christian culture. It was Augustine who gifted the idea of a secular, plural society to the world," he says.

"The idea of 'protecting Christian culture' awakens a sadly dualistic siege mentality that is not biblical. We are called not to protect our own little religious piece of turf, but to be salt and light in every aspect of culture."

Flannagan sees Farage's Britain-focused agenda as somewhat misplaced. He says we should be wary of UKIP's anti-immigration agenda, the driving force behind Farage's narrative, some of which "is an easy way to play to peoples' worst fears about other races and religions, and nothing to do with a missional desire to see God's will be done and his kingdom come in our nation".

"Our job is to infuse culture with the salt and light of the kingdom. Jesus was fully human and fully divine. He provides our pattern for engaging with culture. Neither escaping it to start our own subculture, nor being conformed to it. Instead working in its midst," he adds.

However, Scott argues that in removing Christianity from our national identity, we risk "massive upheaval and fracturing of so much that has been established over the centuries". The rise of Islam in Britain has a role to play in this, he says, and Farage is right to call for the protection of our Christian heritage.

"Islam as a political as well as religious entity provides a very different worldview and with its growth in Britain we are having to ask some very difficult questions about how or if these different paradigms can harmoniously coexist," he explains.

"What he [Farage] is really saying is that if the Christian heart of our national identity is removed, our Britishness will become unrecognisably different... For this to happen over a comparatively short period would destabilise our lives and communities significantly.

"The vast majority of British people don't want to go through such unsettling change, which explains much of the appeal of UKIP as it offers a future that looks back to and grasps hold of the beliefs and ideology that has defined Britain for so long."

Scott is adamant that despite the "reactionary" nature of Farage's comments, the heart of his message remains important. "The alternatives that seek to compete with this Christian heritage are too alien [and offer] no apparent advantages. If our nation is to retain a sense of unity and identity, then we need common bonds. And it is the centuries of formation with Christianity as the root that provides the biggest bond of all," he says.

"That is why Farage is right to call for its defence, even if his language and methods may be questionable to many. Without Christianity at its core, Britain will be drawn into an identity crisis from which it may never recover."

Whether it's something to be defending or celebrating, 'Christian culture' is likely to be a buzz-phrase in the run up to the election. Rather than letting the language of the 'Christian values' be co-opted by far-right extremists or racists, practising Christians of all political persuasions would do well to think about what sort of culture they would like to see, for the good of all, rather than for the benefit of a few.