Please don't ignore the letters. I did this last year( I'd moved address and it had been a couple of years since I'd heard anything) and they took me to court. I now have a a CCJ that prevents me getting any credit elsewhere. Write back saying you are having financial difficulties and can only afford £X each week/ month. They may ask you fill in a financial assessment form but usually are happy to accept an offer and set up a DD. The only way you can avoid this debt is if its been 6 years since any communication from the company/agencies you owe money to.