According to the Prudential survey, 22 percent of those surveyed said they had concealed an average of £7,800 ($12,789) worth of debt from their partners. The reasons for hiding debt varied; for just over half of those hiding debt, the debt was the result of borrowing money to cover every day living expenses, while a third said they ran up debts due to overspending on an emotional event, such as the break-up of a previous relationship. A further 16 percent borrowed cash to make payments to an ex-partner, such as for child support.
And it wasn't only debts that the survey respondents are telling white lies over - one in four admitted to keeping a stash of cash secret from their partner, with an average savings pot of £4,000 ($6,558). The survey found a fifth of those with a secret stash said they kept the money to pay for something specific in the future such as a car or a dream holiday, while 22 percent kept their money hidden to fund their retirement.
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Furthermore, 13 percent of those surveyed claimed to have never told their partner how much they earned and one in ten claimed their partner has a false impression of their earnings.
Two fifths of those who withheld the truth about their income said their basic salary is higher than their partner thinks, and 31 percent have kept at least one bonus payment quiet. A further 31 percent keep quiet on additional income earned though overtime or 'cash in hand' work.
The reasons for holding back information varied widely. For most (51 percent) the main incentive was to maintain independence. However a generous 29 percent do so to buy gifts for their other halves. More than a fifth said they didn't trust their partner's financial decision making, while 16 percent kept a secret stash to protect themselves financially in case of a split.
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Smith-Hughes advised secretive couples to come clean with each other to avoid financial problems down the road.
"Having those potentially awkward conversations so that both partners get a full understanding of their joint financial circumstances is an important first step for a couple planning for a comfortable retirement," he said.
The research was conducted by Consumer Intelligence from October 2-8, 2013 among 1,996 adults over 40 years of age who currently live with their spouse or partner.
— By CNBC's Katie Holliday: Follow her on Twitter @hollidaykatie