In 1993 there were 1500 divorces granted to couples who had been married for more than 30 years. By 2005 this number had ratcheted to 6000.

What remains of course are divorces granted where the applicant is either male or female. And here's where the real politics of trading partners gets interesting.

Generally, where only one member of a couple initiates the application for divorce it's the female who is the prime mover. Although not by the margin you might expect.

Some 57 per cent of single-applications for divorce are filed by women. Surely this is a premium of just seven percentage points over an equal distribution.

Women seem to have guts and initiative when it comes to changing their circumstances, whereas it could be said that men do not.

The ladies' response is worryingly predictable.

"That would be right: you lot are too lazy to get off your backsides to file for divorce."

Or: "The reason you don't want anything changed is that you've got it too good. That's the problem, I'm too good to you!"

Or words to that effect.

But it's not quite true that men don't show initiative when it comes to changing their relationship circumstances. It just takes our gender a little longer to get into gear.

There is a gender swing in single applications for divorce that correlates with the length of the marriage.

The bottom line is that women are more likely to file for divorce in the early years of marriage (when they are young and beautiful) whereas men are more likely to file for divorce much later in life (when they may be paunchy but they are at the peak of their financial and/or career power).

The numbers for 2005 are instructive. Women's dissatisfaction with their marriage peaks in the third and fourth year, when they comprise 63 per cent of single applications for divorce.

By this measure women are 13 per cent more pissed off than men at this stage of the marriage.

Based on the fact that the average woman marries for the first time at the age of 28, this must mean that those who are most dissatisfied with their partners right now are aged 31 or 32.

(The problem for these divorcing women is that they re-enter the relationship market slap-bang in the middle of the man-drought years.)

But the ages of 31 and 32 are the years of the actual divorce.

Separation must have been in place for at least 12 months prior to that date, at the age of 30 and 31.

This also means that the problems that led to the divorce must have surfaced at least, say, 12 months prior to the beginning of separation, at the age of 29 or 30.

This logic process tracks women's problems with their relationship back to the year after the end of their honeymoon.

Men, on the other hand, are statistically less likely to initiate divorce than women for 26 years of marriage. Based on the average age of male grooms 26 years ago, this takes the tipping point for today's dissatisfied husbands to 50.

Ladies, beware: that balding paunchy baby boomer husband sleeping and snoring on the couch could well be plotting a perky partner trade-in.

Beyond the age of 50 baby boomer men finally drag their sorry fat backsides off the couch and into action. In fact, after 30 years of marriage 55 per cent of single applications for divorce are filed by men. Men of this age are 5 per cent more pissed off with their relationship than women.

Now why do you think men would wait so long to end an unhappy arrangement?

Or was it unhappy until that "home-wrecking tart" came along?

Perhaps the answer has something to do with the longevity of tradable sexual power. When a new marriage turns sour, perhaps as early as a year after the end of the honeymoon, women want to ensure their transition to another relationship while they are still "young and beautiful".

Men don't seem to be as concerned about the value of their currency in the process of relationship trading.

After all, men's logic is that there's plenty of time to pick up a trophy wife later in life.

Men's relationship power extends beyond a taut 20-something six-pack and into the 50-something slab. At 50, men can, and some obviously do, trade their partners in for newer, sleeker, racier, models.

And if you remain doubtful about this very modern re-partnering process, consider the following evidence. In 1993 there were 1500 divorces granted to couples who had been married for more than 30 years. By 2005 this number had ratcheted to 6000.

The fact is that long-term baby boomer marriages are much more likely to end in divorce than were long-term marriages in preceding generations.

This is not to say that baby-boomer marriages are more successful; it's just that boomer men are more likely to do something about it.

This in turn suggests a generational shift in values: whereas the depression generation was prepared to slog it out in marriage until parted by death, the boomer generation is more likely to go solo into old age than to suffer the pain of an unhappy relationship.

Bernard Salt is a partner with KPMG