I would ensure that you get legal and proffessional advice on this issue. Phone your local CAB office on Monday.
You don't want to get a CCJ on your account. Have a read of this :
www.direct.gov.uk/
en/MoneyTaxAndBenefits/
ManagingDebt/
CourtClaimsAndBankruptcy
/DG_10013083
This explains it in a little more detail than I could.
I would suggest if you have the means to pay it off, do it as soon as possibel If you have already paid the debt off, contact the company concerned and get written confirmation that you owe them no more money.
"Defaults are recorded on your Credit File when you fail to make Repayments on a loan over an extended period, and the Lender considers it unlikely that you will make further payments.
Having Defaults on your file will certainly make it harder to get credit in the future, but it is by no means impossible."
mypropertyforsale.co.uk/
glossary/defaults.php
You can apply to get defaults off your account. Phone the company concerned and ask them for written confirmation of any contact they have had with you regarding the missed payments. They usually have to notify you 60 days before a default will be added, giving you time to make the payment. They must have copies of any contact with you, if they dont, it is not legal and you can apply for it to be removed via the credit reference agencies (equifax, callcredit, experian) and the company concerned./
My opinions are just that opinions! Always seek legal and financial advice from a professional :)