BRIDES STEAL A MARCH ON MEN; IF IT'S NO GOOD 7 OUT OF 10 WALK OUT :Marriage Files.

She looks the picture of femininity as she glides beautifully towards the altar to the strains of the bridal march.

But the confident bride of the Nineties is much less willing than her mother to put up with her lot when the marriage music turns to discord.

Today's liberated wife knows what she expects of her man - and she is likely to march out of the marriage if she doesn't get it. In two divorce cases out of three, she's the one who decides that it's all over. And she rarely has any regrets about walking away.

True, she is less likely than her husband to have an affair, but if she does, she'll do it out of boredom - or as an act of revenge because he's cheated on her.

The new assertiveness of women within marriage is a key theme running through our exclusive survey.

Until now, no one has been able to say conclusively why Britain has the worst divorce rate in Europe - or explain why more than two marriages in every five are doomed to fail.

We're often starry-eyed when we start out together. But our survey reveals that although Britain is a nation of romantics, the gulf between our idealistic expectations and reality is often too great to overcome.

Love is what leads us to the altar. Boredom, disillusion and temptation are the enemies that lie in wait to tear men and women apart.

Eighty-four per cent of men and women cite love as the main reason for getting married, and for a third of women the desire for security and children rank high. Despite the gloomy divorce figures, the vast majority of couples - 85 per cent of women and 86 per cent of men - expect their marriages to last forever. Yet within a year, more than one in five men feel attracted to another woman.

While 75 per cent of women rate fidelity as "very important", only 61 per cent of men do. Trust is often sadly lacking. More than a fifth of either sex are only "fairly" confident that their partner is faithful.

AMONG wives, 38 per cent say they've been tempted to have an affair. That's nearly as many as men (43 per cent).

Men are more likely actually to commit adultery, though. Fifty-five per cent of divorced women cite their partner's adultery as the main cause for splitting up, compared with 28 per cent of men.

Seventeen per cent of men admit to having an affair, and a further 18 per cent to having a one-night stand. More worryingly, 31 per cent of unfaithful men say they cheated on their wives within a year of marriage.

Women are prepared to stray, too, with 15 per cent admitting to an affair and 8 per cent to a one-night stand. Only 11 per cent of women who say they've cheated had a fling within a year of marriage. In a remarkable reversal of trends, men grow more faithful the older they get, especially once they reach their late 30s.

Wives, on the other hand, are more faithful the younger they are - and those under 27 are least likely to have an affair.

For both women and men - 58 per cent and 56 per cent respectively - the most common reason for adultery is simply an attraction to another person.

For women, the next most common cause is boredom with their husband (40 per cent), followed by revenge (23 per cent).

For men, the second most common cause is a desire for more sex (24 per cent), followed by being carried away in the heat of the moment (22 per cent).

There are enormous regional variations and social factors which influence whether your spouse is likely to cheat on you. Britain's worst husband is likely to be a businessman in his early 20s from the South.

Wealthy Southerners, in fact, are the least romantic people in Britain, and managers and office workers have more affairs than most. Skilled workers are the most likely to have a one-night stand, however.

THE best husband is likely to be an unskilled worker of 40 from the North - provided he doesn't drink.

Northerners are far more likely than other men to have a one-night stand while drunk. Even so, only 9 per cent of them admit to having an affair, compared to 19 per cent from the South and 22 per cent from the Midlands.

Britain's worst wife is a Southerner in her 40s. She's the most likely to have an affair - and to be wealthy, mean and boring as well.

What's more, she is the quickest to break her marriage vows.

Of all the women from the South who have had affairs, 25 per cent were unfaithful before their marriage was two years old. Southern wives, too, are most inclined to have a vicious streak, since only Southern men complain about a cruel or violent partner.

The best wife is a 20-year-old skilled worker from the North. Wives from the North are significantly more faithful than their counterparts in the South and Midlands.

Northern women also seem to make the best lovers - their men are most likely to list sex as one of the best things about their marriage.

But with so many marriages going wrong, why do so many people still bother to tie the knot? It seems it's companionship rather than sex that is the most important reward.

Sixty-two per cent of women and 72 per cent of men say companionship is the "best thing" about their marriage - only 10 per cent of women and 12 per cent of men cite sex. For both sexes, the "worst thing" is feeling that marriage is not enough fun - 18 per cent for women and 17 per cent for men.

When it comes to choosing a partner, 67 per cent of women and 63 per cent of men say a sense of humour is the most important factor.

LOOKS are important for 47 per cent of women, compared to 68 per cent of men - which may explain why men are quicker to cast a roving eye.

Sex is a thorny issue. Just 38 per cent of women and 36 per cent of men say love-making is better after marriage.

Fifty seven per cent of married women say they are too tired for sex, 42 per cent just don't have that loving feeling as much as they used to, and a third are bored with their husbands.

Seven per cent of married couples say they have sex every day, while 34 per cent make love two or three times a week.

Only half of couples think they spend enough time together. Forty per cent go out together just once a month or less, and only eight per cent say they see too much of each other. Money is the biggest cause of rows (39 per cent).

Other reasons cited are time spent together (17 per cent), children (16 per cent), housework (15 per cent), the in-laws (12 per cent) and sex (7 per cent).

Most people know you need to stick at a relationship to make it work - but women are more likely to call time on a failing marriage.

Of divorced women, 67 per cent say they were the ones who asked for a divorce, compared to 36 per cent of men.

Fifty-four per cent of divorced men think they would still be married if only their wives had been more understanding.

When things do go wrong, women have fewer regrets about ending the marriage. Only four per cent say getting divorced was a mistake.

And divorce is at the centre of the most telling revelation in our survey. Unlike our grandparents, few of us now believe that marriage is for ever. If ours is failing, we want to call it a day and look for happiness with someone else.

Seventy-five per cent of men and women think it is better to get divorced than stay in an unhappy marriage.

Julia Cole of the marriage guidance organisation Relate said last night: "This survey brilliantly shows what is happening in Britain today, and we can all learn a great deal from it.

"I think it clearly reveals that women have a far greater fix on reality than men when the romantic idealism wears off.

PERHAPS that explains why men are more likely to have affairs and go in search of other women who always look good and with whom they can have great sex without shattering their romantic illusions.

"You wouldn't be human if you weren't attracted to other people after marriage, but there is a huge difference between thought and action.

"But women are more assertive, demand better deals and won't put up with straying husbands. They won't stay in a marriage that isn't working. They'll get out.

"I think it's very sad that British couples find married life so boring rather than relish the benefits that come from stability and security.

"Too many people see marriage as a kind of entrapment - I think we are probably reaping the seeds sown in the Sixties, when marriage was seen as passe and limiting.

"What this survey indicates is a need for more education. Young people need to be taught relationship skills to help them cope with the problems they will encounter.

"However, it is very heartening that 85 per cent of people go into marriage thinking it will last forever.

"Too many people think: 'That's it. I've got married, I can be happy now'. Then they suddenly wake up and think: 'What next?'

"They need to realise that the wedding should mark the START of all the hard work that goes into a relationship - not the end."