Fresh evidence of "out of control" payday lenders failing to act responsibly and hounding people for money was released by a debt advice charity today.
Citizens Advice said it had seen cases in recent months which included payday lending to people who were aged under 18, had mental health issues or were drunk when they took out the loan.
The findings come at a time when Britain's biggest payday lenders are under threat of being put out of action if they fail to prove to the Office of Fair Trading (OFT) that their practices are up to scratch.
The OFT is expected to announce whether it will refer the payday market for an investigation by the Competition Commission in June.
Citizens Advice said the OFT must take "tough and immediate action" after the trading watchdog handed 50 payday lenders a 12-week deadline in early March to prove their good behaviour or risk losing their licences, which they need in order to trade.
The OFT has written to lenders in waves, telling them where they need to step up, and the responses will be analysed before it decides what to do next.
The Citizens Advice analysis came from 780 cases reported to it between November 2012 and May this year.
It also found that people were being chased for loans they had never taken out and customers were being "hounded" at their home to shame them into paying up.
Struggling borrowers' bank accounts were being drained of cash "without any warning" by lenders using a type of payment agreement called a continuous payment authority (CPA), the charity said.
It found evidence that in some cases, lenders also took more than they were owed and refused to give a refund.
Citizens Advice also looked at customer feedback on 2,000 payday loans from more than 100 lenders, which was provided between November and May.
It said that in almost nine out of 10 (87%) cases, borrowers were not asked to hand over documents to show they could afford the loan.
Three-quarters of people questioned said that they struggled to repay the loan and 84% of people with repayment problems were not offered the chance to have their interest and charges frozen.
Citizens Advice chief executive Gillian Guy described the payday loan industry as "out of control" and said it has shown a "complete disregard" for customers.
She said: "It is vital that, following the investigation, the OFT takes swift action to protect consumers from the harm caused by these unscrupulous lenders."
Citizens Advice has been calling for high street banks to offer people "micro-loans" as an alternative to payday lenders.
One area it found where the charity found payday lenders have improved was in explaining how much the loan will cost.
In 79% of the 2,000 customer feedback cases, lenders were being much clearer about the total cost of the loan.
The OFT's own probe into the industry uncovered evidence of "widespread irresponsible lending" and it found that lenders appeared heavily reliant on struggling customers who cannot afford to pay their loans back on time.
The trading watchdog found that almost half of lenders' revenues come from loans which have been rolled over or refinanced.
The OFT said it has received confirmation from 48 out of 50 lenders that they intend to prove to the regulator that they are acting within the rules.
An OFT spokesman said: "Of the 50 payday lenders that were inspected during the compliance review, 48 have confirmed that they will provide the OFT with proof that they are fully compliant, while two have surrendered their licences.
"The OFT has also announced that it has formal investigations open into the practices of three payday lenders and, in addition, three payday lenders have also had their licences revoked since the review of the sector in March."
Payday lenders recently signed up to new codes of practice to improve affordability checks and make sure customers understand the costs involved.
Earlier this month, payday lenders pressed MPs not to bracket all their customers as being "vulnerable".
The Consumer Finance Association (CFA), which represents short-term lenders, presented a report on their customers to a gathering of MPs in Parliament, which argued they were generally "intelligent, financially-savvy consumers".
The report, titled Credit Crunched, found that more than one third (34%) of payday borrowers had an income of between £10,000-£19,999.