Around a third (33%) of the UK adult population have used buy now, pay later schemes, Which? estimates.
The consumer group, which surveyed thousands of buy now, pay later (BNPL) users, said its findings challenge the stereotype of customers always being young adults who are looking to keep up with the latest fashion trends.
Some people are using BNPL schemes at stressful or challenging times in their life and could be at risk of harmful consequences, it warned.
Its research suggests that missing a credit repayment or bill or experiencing a major life event – such as getting married, having a baby, moving home or being made redundant – increases the odds of using BNPL by around a third (38% and 35%, respectively).
People with dependent children are 71% more likely to have used payment schemes, it found.
BNPL schemes, which are often presented as payment options on retailers’ websites, allow people to spread the costs of their purchases over a period of time.
They may help people to avoid using more expensive borrowing options.
However, the industry generally has faced criticism, amid concerns that some people may end up spending more than they intended and struggle to make the repayments.
Citizens Advice has previously raised concerns that, for many people, schemes can be a slippery slope into debt.
BNPL providers include firms such as Klarna, Clearpay and Laybuy.
Use of BNPL has grown rapidly during the coronavirus pandemic, Which? said.
Two-fifths (42%) of survey respondents who have used schemes have done so in the past year.
A quarter (26%) who had used BNPL in the past 12 months did not think they would be likely to be able to cover an unexpected expense of about £500 using credit. This compared with just a fifth (18%) of the general population.
Four-fifths (81%) of users had never missed a repayment.
People aged 39 or younger were more likely to report having missed a BNPL repayment. And three-quarters of those who had missed a payment had experienced a challenging life event in the past 12 months.
Rocio Concha, Which? director of policy and advocacy, said: “There should be no further delay to plans for regulation, which should include much greater marketing transparency, information about the risks of missed payments and credit checks before consumers are cleared to use buy now, pay later providers.”
Which? surveyed more than 4,600 people who had used BNPL schemes.
Alex Marsh, head of Klarna UK, said: “Fifteen million consumers in the UK have chosen to use Klarna to make purchases, and over half of them tell us they think Klarna is a better alternative to credit cards.
“We don’t charge fees or interest, which saved British consumers £76 million in credit card interest last year. We conduct eligibility assessments, which include soft credit checks, every time someone uses Klarna, unlike credit card firms who check annually at best. This is why our default rates are lower than credit cards at less than 1%.”
Clearpay said: “Unlike many BNPL providers on the market, Clearpay enables responsible spending and our inbuilt protections mean that customers cannot continue to accrue debt or fall into a revolving debt trap. We do not sell debt or charge interest, late fees are capped, and we automatically pause an account if a single payment is late.”
Andy Harding, Openpay UK managing director, said: “We believe all credit products need to be used responsibly which is one of the reasons why we ask customers to make the first payment up-front.
“Openpay does everything it can to help customers meet their payments.”
Gary Rohloff, co-founder and managing director of Laybuy, said: “We check a customer’s creditworthiness and we typically reject around 25% of people applying to use Laybuy. Our customers on average are around 33 and spend £65 per transaction.”
Samantha Palmer, managing director of Payl8r, said: “Lending responsibly and ethically is at the core of everything we do.”