Being asked to be a godparent is an honour. But what does the job actually involve in a society that is increasingly secular? What if you're not religious – should an atheist just say no?

Kate, we'd love you to be Matthew's godmother," said my friend Caroline last week, referring to their 12-week-old son. My stomach tightened. Don't get me wrong – I really want to. It's an honour of the highest order. The problem is that I'm an atheist. So, what to do?

Caroline, who is a Christian and a friend since school, knows this about me. Just as my cousin – also a Christian, who asked me to be godmother to her daughter a few years ago – knows. As I think about it, I relax. I just have to mumble a few words in church, see Matthew have his forehead sprinkled with water, then let the fun begin. I wouldn't be the first non-believing godparent, nor the last.

But then I think about the ceremony and the knot in my stomach returns. "All men are conceived and born in sin." Christening is about sanctifying the child and washing away the sin so that he can be received into Christ's holy church. Well, I'm sorry, but there is little that is more pure than a new baby, and all this talk about the devil and sin and carnal affections in reference to a tiny infant sits very uncomfortably with me. I'm with Richard Dawkins when it comes to children and faith – you can't say a child is Christian, as baptisms appear to do, merely that they are a child of Christian parents.

I tell my friend this, perhaps a little more gently. It is agreed that as it's the nature of the role that is ultimately what counts, it's fine for me to attend the christening without taking part. In my cousin's case, she omitted to tell the vicar there was a third godparent, and in my friend's case, she plans to ask the vicar to allow for the fact that there's an atheist in the mix.

Excellent. Job done. But is it? What, actually, is my role after that? What is any godparent's role within a family? And is there any point, in these ungodly times, in having godparents?

Doubtless, some will say I have no integrity. As its name suggests, a spokesperson from the Church of England points out, at the heart of the role is a commitment to support someone in the journey of faith. An atheist can be a wonderful influence in a child's life, but being a godparent is to be a representative of the religious community and an example of godly living (which is why they should be baptised and preferably confirmed), in addition to supporting them socially.

But even he admits the role has become increasingly ill-understood since godparents are rarely called on, these days, to oversee a child's religious upbringing or bring them up in the event of both parents' death.

At the other end of the spectrum, are the parents who insist they won't expect much and that it's just a good excuse for a knees-up. But I don't think just giving a silver-plated spoon will swing it these days. In most cases, there is an implied understanding that being a godparent is no light undertaking and there is much more involved – even if the parents are not sure of what.

Such parents may not even be religious. The words, "I'm sorry, I'm an atheist", are increasingly likely to be greeted by a jovial: "No problem, so are we."

Any disapprovers might do well to remember there are those with far more questionable intentions. Many a church is packed, with godparents duly renouncing the devil, when it's a mere pantomime to get the kid a place at the local church school. It can also be no coincidence that the super-wealthy boast a far higher proportion of godchildren than most (Elton John is reported to have 10, the Queen 30).

I think back to my own godparents for some clues about the meaning of the role. Plenty of people wouldn't know their godparents if they saw them in the street, but I was lucky. The first, Diana, was a friend of my mother's, of whom I was fond. Tragically, she died of cancer when I was 10, but she did her bit – buying me "unbirthday" presents throughout the year, and taking an interest in everything from Brownie camp to my favourite dolls.

Number two, Elizabeth, is my father's cousin's wife and she still makes a beeline for me at functions. She's a warm, thoughtful person, whom I like enormously. But have I seen any more of her, and got anything more out of those times, than I would otherwise? I'm not sure. The same could be said of the third, Douglas, my mum's cousin. In fact, I've hardly seen anything of him, but his birthday and Christmas presents were always a treat, and I enjoy chatting when I do see him.

Despite my own religious upbringing, and all of theirs, none of them decided theological instruction was their role, besides the obligatory Bible, for which I'm grateful. But what they did was show a heartfelt interest in me and my development. I liked that. It felt special.

What do the people who asked me to fulfil the role expect? And why did they ask an atheist? Caroline says that although she has a strong Christian faith, she thinks it's irrelevant whether her children's godparents are religious.

The church feels like the right place for an event to celebrate her children's life and to name them, she says – a bit like getting married. It adds seriousness, and a sense of ritual, not to mention an introduction to Christianity. "But we've chosen our children's godparents on the basis of having similar family values to us – people we think would make a good guide, or sounding board to our child in times of need," she says. "We've also chosen people we are close to, and with whom we hope to stay in touch – who will be a kind of extended family. We have friends who are very religious – far more religious than me – but we feel having the right person is more important."

My cousin Melanie, also a Christian, agrees: "The ceremony is a chance to say thank you to God and a prayer to look after our child. But when choosing godparents, the priority was people who understand what we're about as a family and who can add something to their lives, perhaps a different perspective. In fact, we waited until our children's personalities showed through, and matched people we thought would complement them."

In the UK, non-religious alternatives have seen an increase in popularity. Two-thirds of local authorities offer naming ceremonies, as does the British Humanist Association. Its head of ceremonies, Ben Siegel, says: "In the past, many non-religious people would have gone along with a christening to keep the relatives happy or because there were no other options. But now there is a ceremony that focuses on family, without the church, and in many cases, people use this ceremony to recruit people to take a special role in their child's life."

There is a range of new terms for such a role: oddparents, goodparents, guideparents and friendparents among them. Sometimes I wish I'd taken this option with my children. They're three and one and we chose guardians, assuming they would get the message about the influence we hope they'd have on our children.

Emma, a friend who has asked my partner and me to be guardians to her children, agrees. "I have good enough friends to know they will be involved in my children's lives in all kinds of different ways, so I have no need to put a stamp or label on any of those relationships," she says. "But I did need to know if something happened to us, there were particular families we could count on and, when you think about it, the kinds of things you look for in those families probably are the same kinds of things you'd look for in godparents."

I have concluded that I'll probably always feel uneasy about the religious aspect of godparenting. I can't help but feel hypocritical. But while I admire people who turn down the role for this reason, I don't believe I'm favouring flattery over my principles. I can safely say that once the last sausage roll is eaten, I will feel an enduring and important legacy, just as I did with my previous goddaughter.

My policy is to ditch the nonsense about silver spoons, to send random presents and take them out for fun treats until they are 10. Then, in their teens, I hope to keep the lines of communication open and let them know I'm around if they want me, but respect them if they don't.

By the time the children are adults, my hope is that they might want to know me, not just as mum's friend or relative, but because we have built up our own bond.