Of the partners caught in the act, 29% were hiding credit card debt, 25% were hiding loans, while 21% had missed bill repayments.
Julie Doleman, managing director of Experian Consumer Services, said: “It takes a while for any couple to feel comfortable enough to discuss their finances.
“However, if you are planning a future with the person you love, financial honesty is important.
“Understanding the impact of your past spending and borrowing habits will help you see the way forward to realising your aspirations, be it buying a home or even starting a family.”
Poorly managed debt can have a long-term impact on a couple’s finances, as credit reports become linked if they take out a joint bank account or mortgage.
Currently 36% of Britons have such joint credit agreements.
Of those surveyed, one in 10 has had to postpone taking out a joint credit agreement – such as a joint mortgage – because of their partner’s credit score.
Doleman added: “Sitting down together and checking both of your credit reports will give you a good overview of your current financial situation, and will help guide you in making any improvements necessary before you might need to apply for credit in the future.
“Taking the time to understand how you can improve your credit scores now could make a big difference to your bank balance in the future.”
Financial problems can also put a strain on the relationship, as more than a quarter of couples (27%) admit they argue over money, with spending the most common cause of rows (51%), while 7% of Britons have broken up with a previous partner over money matters.
Men are bigger secret spenders, admitting that they would happily spend £344 compared to £265 for women without discussing it.