Sorry to bump such an old thread, but hopefully this information may be of some use.
I will admit to falling into these bastard's traps on more than one occasion over the years. Fucking parasites.
Something I only recently discovered however was that many of these loans should never have been issued because they were unaffordable. For a loan to be unaffordable it needs to meet one or more of the following criteria...
1. you often rolled loans or borrowed again soon after repaying a loan;
2. your loans from a lender were increasing in size;
3. some repayments were late; or
4. the loan was a significant part of your income
If a loan is deemed unaffordable then you can complain to the lender and request a refund of all interest paid on the loan, plus a statutory 8% on top. Now most of the lenders don't just hold their hands up and pay out. You have to lodge an official complaint and in most cases refer your complaint to the Financial Ombusdman, but it appears this type of complaint has a higher success rate than any other from the FO. All the details of how to complain including templates are here...
https://debtcamel.co.uk/payday-loan-refunds/Hope this helps someone