As many as 4.5m Britons could be concealing secret savings from their partner, amounting to a total stash of £4.6bn.
The research, by financial services giant, Prudential, found that 15% of Britons aged over 40, who live with a partner, are hiding savings worth over £1,000.
Women are more likely to squirrel their money away with 18% admitting to hiding savings worth an average of £1,002. In comparison, 12% of men are concealing funds worth the slightly higher amount of £1,072.
Almost a quarter confessed they were hiding their money away in case the relationship ended.
Vince Smith-Hughes, head of business development at Prudential, said: "While it is understandable that some people in relationships want to be able to spend their own money, it is important for couples to have regular and open discussions about financial planning for the sake of maximising their retirement incomes."
Trisha Doyle, Editor of AOL Money, told The Huffington Post: "The dynamics of relationships in terms of money are changing as, in most cases, both partners are now working in contrast to say 50 years ago. Both partners have probably worked incredibly hard for their savings and are aware of each other's shortcomings when it comes to finance so it's understandable that money is being squirrelled away for a rainy day."
She adds: "It's fair to say that relationships don't always last forever so keeping a savings pot just for yourself can be a comfort to people who have been burned in the financial stakes when a relationship ends."
But while Doyle understands the desire to look after your own interests, she stresses the importance of setting down some rules for your relationship and money. Here are her top three tips:
- Set guidelines. Agree who will pay what and also, importantly, when. Saving the money is great but making sure bills are paid on time is vital too, so try and dole out those tasks evenly.
- Join forces. Many couples choose to have a joint account for household-related finances and this can be useful to keep a track on expenditure. It can offer a degree of independence for couples, particularly before kids come into the equation.
- Be open. Being able to talk honestly about finances and letting your partner know where you stand financially can really help to develop a good attitude toward money for your relationship. It's one of the biggest stresses on relationships, so having an open and honest dialogue can help overcome any bumps in the road in the future.