It was a gift to headline-writers. Pope John Paul II, it turned out, had a 32-year "intense friendship" with a married woman. They exchanged secret letters. "What really happened between Pope John Paul II and his close friend, Anna-Teresa Tymieniecka?" asks one headline, setting you up for some really juicy revelations.

Scandal-hunters were disappointed. The friendship was just a friendship. The letters weren't secret, just private. And what really happened was nothing untoward at all. Yes, they were close and very fond of each other, but they were just good friends.

It was a pity for those seeking ammunition against the Church, but rather heartening for others. It was perfectly possible to be a Christian – even a celibate Christian leader – and have a normal friendship with someone of the opposite gender.

It's a question that's been asked for years, and not just in the Church. It was the theme of a famous 1989 film, When Harry Met Sally, starring Billy Crystal and Meg Ryan: can men and women ever be just good friends? As Harry says: "What I'm saying is – and this is not a come-on in any way, shape or form – is that men and women can't be friends because the sex part always gets in the way."

But does it? Not according to a book by Joshua Jones, a missionary with World Horizons UK. In Forbidden Friendships: Retaking the biblical gift of male-female friendship he argues that Christian men and women can indeed be friends.

It's a brave thesis. Jones argues that in evangelical churches particularly, there's been "a growing relational chasm within the church that seeks to keep men and women from engaging in genuine friendship. This separation has been parading under the banner of integrity and it has become unhealthy."

He continues, "Not all agree with the new boundaries which keep men and women apart. But those who disagree often fear to raise their objections."

Jones argues that friendship between people of the opposite sex, whether married or not, is normal and healthy. He says it's part of being a fully-functioning Christian community. Our suspicion of it is basically worldly, he argues, arising from a preoccupation with sex under the influence of Freud: "It is now assumed that any meaningful interaction between a man and a woman must involve some pursuit of sex, making real friendship impossible." This goes along with a culture of blaming women for men being tempted and setting rules to keep them apart.

For Jones, it doesn't have to be that way. Cross-gender friendships can help defend against temptation and keep marriages strong. They don't have to be threatening and people like Mark Driscoll, who says that "having as your close friend someone of the opposite sex who is not your spouse" is "emotional adultery", have got it wrong. Jones gives biblical examples from the lives of Elijah (1 Kings 17) and Elisha (2 Kings 4:8), not to mention Paul (Colossians 4:15) and the Lord Jesus himself. There are plenty of examples from Church history, too, such as the Celtic Church where an "anamchara" – a 'soul friend' or spiritual mentor – might be someone of the opposite gender.

Of course there are emotional risks, and Jones addresses those. But there are always risks in friendship, he says, and our lives are much richer and fuller if we open ourselves to to the gifts that an opposite-gender friend can offer.

Is he right? I'd like to think so. The premise of When Harry Met Sally is that, in the end, sex does get in the way. But that's a worldly film, and romance sells. Pope John Paul's experience, and that of many others, is that it needn't. It's very hard to define and the boundaries do tend to blur, but there are masculine and feminine ways of thinking and feeling, and perhaps to be really well-rounded human beings we need to be able to draw on both.

For single people, friendships with people of the opposite sex can be deep and enriching. For married people, it takes trust, openness and maturity. But the idea that someone's automatically being unfaithful to their spouse if they become friends with someone else needs to be challenged. Friends of whatever gender can surely be just good friends.

Follow Mark Woods on Twitter: @RevMarkWoods