A money lender has to be accepted by the Financial Conduct Authority (FCA) to lend money legally. Those who are not are breaking the law. They are called loan sharks.
They often work from home, charge high rates of interest and do not give you much paperwork. They might have lots of customers and lends money like a business. But it is illegal.
They might do other illegal actions. Such as threatening violence or taking your credit cards or valuables. In extreme cases, they have been known to force non-payers into prostitution and drug dealing.
To see if someone is legal, use the Finacial Services Register.
If you spot a loan shark or you have borrowed money from one you can report them anonymously by phone 0300 555 2222 or email ReportALoanShark@stoploansharks.gov.uk.