I'm not sure that Themas is right.
A debt is considered Statute Barred if a creditor has not contacted a debtor for a period of 6 years and no action has been taken on the account.
Although the debt is still legally acknowledged as being owed, the creditor is not able to take any legal action against the debtor in order to recover the debt.
It is considered unfair if a creditor or debt collector misleads the debtor into believing the debt is still legally recoverable. It is also considered an unfair practice if the creditor or debt collector press for payment after the debtor has stated they will not be paying the money owed.
This could amount to harassment contrary to Section 40(1) of the Administration of Justice Act 1970.
I suggest you write to the DWP, quoting the Freedom of Information Act, to get all the notes and info on your account - which will show if they have have tried to contact you in the preceding 6 years.
Make sure that everyting you do is backed up with copies and send everything in the post by recorded delivery.
Once you've posted it, if you can also fax it and keep the header sheet, it will reinforce your case considerably.