You know how it is, being married. Everything is proceeding normally - odd socks in the laundry basket, shaving gel in the sink, he does the shopping and comes home with a stack of chocolate biscuits and frozen pizza - and then one day, out of the blue, you get a phone call and a woman you never knew existed asks: "Are you married to my husband?"
OK, maybe "normally" is the wrong word. But when Maria Barrett began to look into double lives and related topics by way of researching her fifth novel, Intimate Lies, she was surprised to find that - across a whole spectrum of situations, from long-term affairs to long-term commitment to two partners, to actual blatant bigamy, there's a lot of it about. "I honestly thought I'd find one case, or maybe two or three," she says. "I found seven." It started when she heard a story "through a friend of a friend of a friend" about a man who had led a double life with two separate women in two different parts of England. "And I was so fascinated, not just by the logistics of how he could have done it, but also the psychological thing of why, that I decided to try to contact him. I told someone I'd really like to talk to him, and then the word got around, and finally he rang me. It was all over and done with at that stage, because he had been found out, so he actually wanted to talk about it."
In Intimate Lies, a featherlight romantic thriller, a man is believed to have committed suicide when his belongings are found on a beach. The police, however, are baffled when two sets of missing persons forms are filled in, identical in every respect except for the address and next of kin - for Alexander Turner appeared to have had a wife called Jill, complete with two children, in Brighton and a wife called Holly, who runs an art gallery in London. In fact, according to Maria Barrett, because of the ease with which it's possible to get married in the UK, such a deception is not at all difficult.
"It's actually easy to do - all you need to get married is a piece of paper saying that you've lived in a certain area for a certain length of time. That's it. No passport, no birth certificate and there are no computer records. You could literally do it in a different registry office every day of the week."
It's now so commonplace for people to live together without getting married, however, that bigamy as such has been steadily decreasing over the past 50 years. Seventy years ago, one in seven cases brought to the British Crown Court was for bigamy, whereas in 1995 just 15 people - 10 men and five women - were convicted of the crime, which carries a maximum prison sentence of seven years. "The main reason for prosecution in Britain today is if either social security fraud or marrying to get British nationality is involved," says Barrett.
"One of the people I spoke to was a serial bigamist - she had been married 10 times and four of those marriages were bigamous. "This woman actually gave herself up at one point - she had been married three times in six months and was so confused and distressed that she went to the police and said she needed help. "They virtually laughed her out of the station - they just weren't interested, because she had done it for emotional reasons, personal reasons. There was no financial gain involved. In the end, more or less at her insistence, they prosecuted her, and she got a seven-month suspended sentence."
Not that it solved her problem; the woman subsequently married bigamously once more, was divorced twice - and finally found happiness with her current partner. Perhaps she had run out of wedding dresses? Well, says Barrett, in this particular case there were, if not extenuating circumstances, at least explanatory ones. "Her parents turned out to be her grandparents and her sister turned out to be her mother - which she found out at 16. Then when she went to confront her mother several years later, her mother was killed about two weeks before she was due to speak to her, so she had never been able to lay that to rest."
In most of the cases she encountered, Barrett says, the scale of the duplicity was awesome. "With all of the people I spoke to, dishonesty was such a major part of their lives that you'd imagine they'd have to have some sort of personality disorder to cope with it. I mean, it's miles away from telling the odd porky pie, isn't it?"
One man had two separate families, one in Norway and one in the UK, and neither family suspected anything was amiss. Then there was the middle-aged housewife who lived a normal life as far as her family and friends were concerned but who, during the day, travelled to London, picked up men and engaged in bizarre antics such as having sex in the cloakrooms of golf clubs. "But I think the worst was this young man Mark, who had a partner in one part of the country and a wife and baby in another. He would do things for his wife, such as leave little notes on her pillow saying `I love you - can't wait to see you next Tuesday' and then take off, ostensibly on business, and then between Saturday and Tuesday he was up north with this other woman he shared a flat with.
"With his wife, he was the perfect family man - stayed in, watched TV and looked after the baby - and with his other partner he'd go out windsurfing and had a different set of friends. "One was a very secure, domestic type of environment; the other was outgoing, dynamic, sexual. It went on for two years, then his wife found out and blew the whistle, and both women dumped him.
"In a way, he was relieved - but he was very upset that he had lost both partners and quite shocked at how devastated they were by what had happened. He didn't know what he had done wrong."
Despite the elaborate nature of these sexual frauds, the bubbles all burst in the end - and almost always because of some dull, small detail: a dry-cleaning stub from an unfamiliar town; a credit-card slip for an unexplained dinner for two. It was the latter which caught Mark, whose attention to detail had been so thorough he even had two separate mobile phones for his two households.
But what about money? Wouldn't it take considerable resources to maintain a full time double life over a period of years? "Well, one thing I did find was that quite often the women paid," says Barrett. "The second women, especially, tended to be either equal partners financially or - in some ways - the breadwinner. In one case I spoke to the bigamous second wife, who had been supporting her `husband' because as far as she was concerned he was unemployed and off looking for another job, doing interviews, etc. It never occurred to her that he was really visiting his other family until, three months into the marriage, she was phoned up by his other wife, who said she had heard there was something going on."
Something going on, indeed. "He went through the whole wedding scene - I find that incredible, actually - that someone could go through an entire engagement, the booking of the registry office, the party, the works." Barrett was shocked by some of the discoveries she made - and surprised, in the end, by what shocked her. "First of all I began under the misconception that these people must be stark raving loonies - you know, that you'd be able to see them coming or something. But you can't. On the surface they seem really normal and nice; which gives you a completely different perspective on life; a certain wariness creeps in.
"But more than anything I find it very, very upsetting to think what sort of damage it has done to the women who were deceived. Not just in terms of not trusting another partner - but not trusting anybody, ever again, about anything. Even something as simple as, you know, if somebody says, `hey, you look nice', how can you be sure they aren't really saying `God, you look awful'?"
Intimate Lies is published by Warner Books (£5.99 in the UK).