Three quarters of couples (73%) surveyed claimed to shared every detail of their finances with their partner but 15% said they kept some aspects of their financial lives private, often information about savings. 

One in 20 (4%) people say they had agreed to share everything with their other half but admitted lying. 

Some 7% said they tell their partner everything about their finances but they think they are being lied to. 

Some 10% of young people aged 18-34 think their partner is lying to them about money.

Married people were more likely to agree to share everything but were also more likely to lie to their partner about their finances than those who live together. 

The most common lie is about how much savings each partner has with 48% admitting lying about this. Women lie about spending, debt and income more than men do. Among those who admit lying, 35% of women say they lie about spending compared to 14% of men.

The survey was carried out by Hargreaves Lansdown for National Marriage Week which starts on 10 May. The data comes from a survey of 2,000 people by Opinium for Hargreaves Lansdown carried out in April.

Sarah Coles, personal finance analyst, Hargreaves Lansdown, said: “Marriage means we’re more likely to agree to tell our partner the pure, unvarnished truth about every aspect of our finances. It also means we’re more likely to lie about it - particularly when it comes to savings and debt.

“There’s nothing wrong with the odd white lie about a trivial and inexpensive purchase. There are also plenty of couples who have an emergency fund they keep to themselves, so if something goes wrong, they have something to fall back on. 

“However, if couples get into the habit of lying to one another about important money matters, it can cause all kinds of problems over the longer term. It can mean missed bills and dangerous hidden debts, and it can test a relationship to breaking point.”