The affair may begin at David Jones, when a woman spies a Balenciaga number. She destroys the receipt and passes it off to her husband as a sale frock. Or the illicit fire may spark at Bunnings, when the latest cordless power drill beckons a bloke. He hides his prize in the garage, away from his wife.

Committed couples may share a bed, yet some draw the line at mixing love and money. A study conducted last year on behalf of BankWest of 597 Australians aged 18 to 64 who were married or in de facto relationships found 43 per cent were not willing to share a credit card with their partner - in case they became responsible for the partner's purchases, or revealed their own.

Seventy-two per cent shared a bank account with their life partner and 50 per cent had a joint mortgage. But both sexes in equal measure baulked at sharing the buy now, pay later plastic.

The guilty secrets that appear on credit card statements may require little white lies. In the US last year, a study conducted for lawyers.com and Redbook magazine found 29 per cent of adults aged 25 to 55 had been dishonest with their partner about their spending habits. Women (33 per cent) were more likely to be telling the purchasing porkies than men (26 per cent).

Such subterfuge seems common here and may help explain findings by Relationships Australia in 2003. It surveyed 1215 Australians about the most negative influences on their intimate relationships and found lack of time (38 per cent), lack of understanding (27 per cent) and lack of communication (21 per cent) were all ahead of money problems (20 per cent).

Five years earlier, a similar study had found money rated much higher as a negative influence, at 28 per cent.

The decline of money as a fear factor for Australian couples may reflect the growth in financial independence within a relationship - what you don't know about your beloved's little expedition to Westfield won't hurt you.

Louise Woodger, 33, is about to get married. She intends to keep a separate credit card as a measure of her continued independence and won't always divulge her purchases. "I wouldn't think my partner would want to know everything I'm buying, anyway," she says.

Woodger, a Sydney financial planner, grew up in a family of accountants. Many couples keep separate bank and credit accounts, she says, especially when one partner has been burned before.

For instance, one of her recent clients, a woman from a wealthy family, had been shocked to discover during a divorce that her husband had been borrowing money against her assets without telling her. "Obviously, there are people who are not trustworthy," Woodger says.

Secret stashes, be they Manolo Blahniks or an investment shack in Byron Bay, are important to many, but doubly so to divorcees. "There's probably a fear of not wanting to be vulnerable again by allowing the other person to have control of their financial information," she says. "I think all women like to keep a separate credit card account, though. It happens all the time. I don't know many people who don't like to have some independence."

Woodger says in her experience most couples discuss and co-operate on crucial major purchases, such as items for the house, or saving for a holiday.

Some women, however, still find it difficult to negotiate spending with their partner, particularly when they have taken a career break or given up work to raise children, says Relationships Australia NSW's chief executive, Anne Hollonds. Given many couples now wait until their 30s to wed and have children, both partners have had a longer time than in previous generations to get used to separate incomes, she says.

There are three barriers that lead to partners being less than honest about what they buy, Hollonds says: having few, if any, joint financial commitments in the past; a lack of trust between partners; and a man's traditional or patriarchal belief that he should be in charge of the finances.

In some couples, she says, one partner can use money as a power tactic, leaving the other partner feeling "helpless and victimised". Relationship counsellors call this financial abuse.

Yet the freedom of consumer individualism appears to have created a credit quagmire. Australians are carrying an incredible $36 billion in credit card debt on a record 12.9 million credit and charge card accounts, up from 11.9 million cards last year, according to the Reserve Bank.

We're now saddled with an average outstanding credit card balance 185 per cent higher than a decade ago, even though average weekly earnings have risen just 46.5 per cent, the central bank says. Financial institutions often grant increases to people's credit limits on interest rates up to 19 per cent, without them even applying. It's a worrying temptation for many, given the added pressure of rising mortgage interest rates and petrol prices.

Gay Curtis, the author of Smart Couples' Guide to Money, works with BankWest promoting its Get Australia Saving campaign. She says people have replaced the buzz or feelgood factor of saving with the false thrill that a credit card gives them extra money with which to play. "We live in a spending culture," she says.

Purchases are sometimes made in secret because of differences in choices and interests between the sexes, she says - a man may not understand a woman's shoe fetish and a woman may not understand why a man needs to keep buying new IT gear and DVDs.

"Honesty is the best policy," she says. "If you can't put your cards on the table with the one you love, it's a pretty sad world. If you have to buy things behind your partner's back, I don't think it's the basis for an effective relationship. You need to respect each other's hobbies, goals and interests."

Financial affairs

Money coach Gay Curtis's advice for couples haunted by financial secrets:

1 Together write your individual and shared financial goals for the short, medium and long term. Include hobbies and respect your partner's interests.

2 Work out a household budget. Include a savings plan and perhaps consult a financial planner or money coach.

3 Create a formula to allocate your earnings each week or fortnight: for instance, pay 65 per cent to the mortgage, and split the remainder for living and saving (or a 50-50 split might be more realistic). If you have two incomes, perhaps use one to pay the mortgage and the other to live off and to save. Re-assess outgoings.

4 Decide whether to have joint or separate bank and credit card accounts. Debt on combined credit cards can become a problem if you split. If you keep these accounts separate, be honest with one another about spending and debt.