Christmas is the season for angel sightings, in decorations and on cards. Cute blonde children dress in white and announce peace on earth to unimpressed shepherds at school nativity plays. The angelic host sheds feathers all over the cinema and television listings, from Ben Affleck as a fallen angel in Dogma to John Travolta smelling of warm cookies in Michael.
As Westlife prepares to excommunicate Saint Cliff from the Number One spot today with a song called "I Believe in Angels", uncles drunk on eggnog will be grabbing microphones to sing "Angels" by Robbie Williams, revealed last week as the nation's favourite karaoke tune.
Out in the cold winter air, the Angel of the North looks down on Gateshead, and its stone colleagues watch over Karl Marx in Highgate Cemetery - which is as good a place as any to meet the author of the Good Angel Guide.
"The angels here are very beautiful, between men and women," says Alix de Saint-Andre, inspecting the ornate gravestones. "They are very long and thin, not like our French ones, or the Italians, the children with big bellies."
The small, animated woman with a boyish bob is an unlikely expert on celestial visitors. She is a star herself in France, thanks to a chat show watched by millions on Canal Plus, articles in glossy magazines, and a series of dark-hearted novels - a sort of slimmer, sexier Julie Burchill, a youthful fortysomething. Now she has a bestseller, with a book about angels.
If your heart sinks at the thought of yet another collection of anecdotes by oddballs who swear they really have met one of God's messengers (on the way to see Elvis at the 7-eleven, presumably) then be ye not afraid, as a certain archangel once said around this time of year. Such works are "distressing angel pornography", says Saint-Andre.
"If they are to be believed, angels combine the properties of a mobile, a personal lightning conductor, a pet and Tinkerbell," she says. "So why be without one? Give up the Prozac now and adopt an angel, or even several: there's no danger of them peeing on the carpet. And they can be delivered just in time to calm any metaphysical anguish the Millennium might bring. This is cloud-cuckoo land."
As a young girl at a Roman Catholic school, Saint-Andre was always terrified by the idea of seeing the Virgin Mary in a vision. "She appears to young kids, girls mostly, when they are alone. The only place where I was alone was the toilet, so I never closed the door because I was frightened to have an apparition, and the Virgin Mary telling me, `You have to make a church for me in the garden'. Everybody was saying `close the door' but I couldn't tell them I didn't want to be a saint." She giggles at the memory. "Perhaps that was the beginning of the fascination."
Three years ago she sat down to write a mystery novel set in a Roman Catholic girls school, almost like the one that had dominated her childhood. "Many nuns are killed. And priests are killed also." One of the characters was an angel, which she wanted to be as plausible as possible. So began three years of research, investigating the scriptures and commentaries of Christianity, Judaism, and Islam.
The result is a witty but learned book revealing surprising similarities in what these three major faiths think about angels. "Christian angels come from Jewish ones, of course - Christianity began as a branch of Judaism; and Muslims too have the same angels. Why not? If there is one god ... but they are not treated the same."
Whether you're a believer or not, the Good Angel Guide unravels an arcane subject with wit and wisdom. In France it has been lauded not by the church but by left-wing intellectuals and sceptics, who love the dry, acerbic and irreligious way she explores the sacred. The book explains the ancient origins of all those winged beings that populate our pop culture at Christmas - and tells us, for a start, that they often don't have wings at all in the Bible, the Koran or the Torah. They are usually androgynous beings, neither male nor female - although that doesn't stop them getting up to mischief.
"They are not supposed to have sex, because an angel is a spiritual creature, but we have testimony even in the Bible of angels who found that women were nice and came to earth. The children they had with the women were giants who died in the Flood. There is a tradition, Jewish and Muslim, about these two angels who came to earth at the beginning of the world, to prove to God that man was not a good creature, and that his place on earth should be taken by angels. In fact, these two angels do all sorts of stupidities - they steal, and they teach men how to make war, and women how to seduce men. It's a mess. And it's one of the first stories about the Devil."
Not that Saint-Andre herself would fancy a celestial fling. "Oh no. When I want to have sex I wouldn't think about angels. All those feathers - are you sure? Atchoo."
Some of the angels and archangels she uncovered in scriptures are fearsome, powerful super-beings with blazing eyes and dazzling swords. Many of us no longer believe in any kind of God, and yet the image of the angel as a gorgeous, peace-loving lady-boy with fluffy white wings remains enduringly popular, as you can see all around you this Christmas. Why is that?
"We want to see them like that. We want to have a spirituality - it is the end of the century, we want to believe in something; but something not too big. Not too challenging. People don't like religion any more. It's too tough, too hard. But an angel gives you a little spirituality and it's supposed to be kind, it's supposed to be your best friend. It's nice, you can talk to the angel. You are not obliged to respond, you can still do whatever you want."
The trouble with angels is that they're largely invisible - except when they choose otherwise. On Boxing Day, the Coronation Street actor Bill Roache, better known as his character Ken Barlow, will describe how angels gave him a glimpse of his baby daughter Edwina on the morning of her funeral. "There was this glorious glow," he will reportedly say on an ITV documentary called The Day I Met An Angel. "I call it a glory - a round, glowing light. In the middle was Edwina's face, smiling. I saw it, there was no question - it was not a dream or anything. I knew there was an angelic being helping Edwina to appear like that."
Saint-Andre is doubtful. "I suppose it's real," she says of such testimonies in general. "But there is no way to verify the information. It's like someone drunk who tells you he has seen some pink elephants. It's true, he has seen some pink elephants, but were they there really? I'm not sure."
Her cousin insists on having a very special guardian angel. "She has her mind in the clouds. She's never on time, she has been late from the day she was born, but when she has to take a train she doesn't worry about the time. One day I told her, `Well the train must have gone, it's 10 minutes past.' She said, `No, don't worry, my angel will keep it.' We arrived and the train was not gone. Then there are the strange coincidences. You think of somebody and this person you didn't see for six years will phone you that day."
In the introduction to her book, Saint-Andre admits, "I have never seen an angel in my life. Not even a tiny one. Not a single wing or feather - nothing. Pointless to go on about it."
And yet, looking for angels for three years has taught her to see signs in the littlest things. "I was in the suburbs of Paris, on my way to see the publishers about this book, and I was a little agitated. I was walking and I found a little feather. There was no tree, no bird, nothing. I said maybe it's an angel joke. It doesn't mean anything, it's just [she snaps her fingers]. A smile of God. It just happens. Like the fact that when you talk about angels you will find angels everywhere. We sat here to have a coffee, and the pub next door is called the Angel. They like to have fun. But with spirituality you never can prove it."