The christening of Geri Halliwell's child, Bluebell Madonna, was deemed so significant that it even sparked the reunion of the Spice Girls (or most of them). Stars flocked to St Michael's Anglican church in Highgate, north London, and socialite Lady Isabella Hervey was moved to remark not on the baby's religious induction but on the fact that the mother looked lovely. "Geri looked stunning," she is quoted as saying. "It was good to see so many Spice Girls back together again and getting on so well."

That Bluebell's godmother is the wealthy mother-of-three Victoria Beckham proves again that godparenting is the new rock'n'roll. But what her role will be in the baby's life is anybody's guess. Will God feature in the job he puts his name to? Will Bluebell feel able to confide in her godmother and ask for spiritual guidance the way my older godchildren can with me?

I can vouch for the overwhelming feeling of pride in being a godmother three times over. For me it's a unique privilege in an increasingly secular world. But it's also a hellish responsibility, for I know that I need to be au fait with the dogma of our religion at all times - just in case. Even if you're never required to be instructing the child in religious matters, the relationship between godparent and godchild is blessed.

Halliwell is thought to have chosen Posh as Bluebell's godmother not only because she helped her through her pregnancy, but because the two former Spice Girls remain friends. Elton John's 10 godchildren are all the offspring of his celebrity friends. They include Sean Lennon, Brooklyn, Romeo and Cruz Beckham and Liz Hurley's son Damian.

But friendship between adults is not the best reason to ask someone to be a godparent. Being themselves christened into the same church and living a life of faith are more important if the godparent's role is the Christian one of committing to look after the child's spiritual welfare for life, if the parents fail to do so or if they die. A Catholic godparent is also required to be present at the child's confirmation in order to emphasise the unity of the two sacraments. That's why it's usually relatives or old family friends of the same religion who are asked to be godparents (I am the aunt of two of mine, and the oldest friend of the other's mother). Taking an active part in the Christening ceremony before God emphasises the eternal, spiritual role the godparent will play in the child's life, and avoids the awkward secular problem of what might happen to the child if the adult friends irrevocably fall out before it grows up. After all, godparenting is about the child, not about the adults.

It's not for me to second-guess their religious credentials, but if Victoria Beckham's and Elton John's roles are as mere mentors to their godchildren, then they might just as well be referred to as the fairy godmothers of childhood fiction - the kind of person who will always be in a position to help the child out financially or socially, if they so wish. Perhaps that's the reason Halliwell's friend George Michael, who is understood to be Bluebell's godfather, didn't appear at Sunday's ceremony.

Many see godparenting as looking after the child's material needs should its parents die, though fostering or adoption are subject to separate legal negotiation. A survey carried out by a savings bank found that only 10% of British godparents saw their role as being linked to religion. Most thought of themselves as the child's legal guardian, moral guide or adult friend, and revealed that they spend £3bn on gifts each year.

Should one's godchildren be lavished with more expensive presents than the ordinary children in one's life? Thankfully my own religion advises that financial status is less important than spiritual richesse. I can only pray that my own three darling godchildren will learn to appreciate the difference.