More than 17 million UK customers have now used a buy now pay later (BNPL) company to make an online purchase. The payment method is also set to have its biggest Christmas yet. BNPL firms allow people to manage their shopping, either by postponing their bill for a short while, or splitting it into more manageable chunks over time, interest free. But users too easily end up in debt and tougher rules are needed. Klarna, the biggest UK provider, has seen its customer base double to 15 million since 2020. Other companies, Clearpay and LayBuy, are also expanding fast. The fastest growth is among 40- and 50-year-olds. A recent Citizens Advice survey found almost one in ten plan to use BNPL for Christmas shopping. Citizens Advice urges consumers considering using BNPL to ensure they understand what they are signing up for, how they will make the repayments, and what will happen if they can't pay on time.