Nearly nine million people across the UK are living with serious debt problems, according to a new report.
The Money Advice Service (MAS) also said very few people were making any attempt to get professional help.
The problem is particularly acute in five English cities, where more than 40% of the population is struggling to repay debt.
According to the survey, 18% of Britons, 8.8 million people, consider they have "serious" financial issues.
MAS, which is backed by the government, said that for the first time, the survey had provided a detailed understanding of the lives of those who are in debt.
The report found that 74% of those struggling with debt were "unhappy".
There is particular concern that very few people ask for help.
"Millions of people could escape their spiral of debt by accessing free advice," said Caroline Rookes, the chief executive of MAS.
"We know it transforms lives and the sooner people access it, the better - to take steps to improve their life for good," she said.
The study lists the top five cities where people are "over-indebted".
To qualify as such, people had to feel that their debt amounted to a "heavy burden", or else they had to have missed out on repayments in three of the last six months.
The most heavily indebted area was Hull, where 43.1% of the population admitted they were in trouble financially.
The four other places were also in England: Nottingham, Manchester, Knowsley and Liverpool. All five areas had at least 40% of the population in heavy debt.
"You'd be surprised at how many are struggling," said Ann Jones, a grandmother from Hull.
The BBC spoke to her at a food bank on the North Hull estate.
She took out a bank loan of £2,000, but had difficulty paying it back.
"Everything got so expensive, and before you knew where you were, you just didn't have enough at the end of the month," she explained.
"It's nerve-racking. It's made me really ill," she added.
Latest figures from the Bank of England suggest that personal borrowing, including mortgages and unsecured loans, is now at £1.43 trillion.
That is the same level of borrowing that was reached during the pre-crisis peak in September 2008.