Almost four in 10 people are keeping "money secrets" from their loved ones, including hiding debt problems, the Money & Pensions Service (MaPS) says.
The most common secrets are hidden credit cards (37%), undisclosed loans (23%) and secret savings accounts (21%), the government body said.
Millennials aged 25-34 were the most secretive generation, with three in five hiding details of their finances.
There are "numerous reasons" for it, said Sarah Porretta of MaPS.
"A secret savings account could act as a buffer for those who want to escape a difficult relationship; an unpaid bill could be kept under wraps in order to protect anxious family members.
"For many who keep money secrets, it can be a feeling of shame or embarrassment that debts have spiralled out of control."
The survey, which covered 5,200 people nationwide, suggests there is still a stigma around talking about your personal finances in Britain.
Almost 40% of respondents said they stayed silent about concerns, often due to feeling embarrassed or a fear of being judged.
The survey also found people in relationships tended to underestimate the extent of money secrets their partner kept from them.
While 23% of people in relationships suspected their spouse hid things, nearly half admitted to having hidden things themselves.
'We sorted it'
One respondent, who preferred not to be named, told MaPS: "I was once close to bankruptcy due to credit cards and loans which I did not reveal to my partner until it couldn't be hidden any longer. I admitted the issues eventually and we sorted it."
Another said: "I didn't tell my husband when I lost control of our credit card debt and ended up juggling cards and minimum payments.
"Eventually I admitted it to him and actually acknowledged the amount of debt I now had - he supported me to get onto a debt payment plan which I have been paying for just over a year now, and we are far more financially stable."
The survey marks Talk Money Week, which is encouraging people who are struggling financially in the pandemic to talk it over with a friend, family member or expert.
MaPS says it could help make money problems more manageable, benefiting people's health, relationships and overall wellbeing.
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