Unless you have had confirmation that the debt is written off it is still enforceable, the original creditor or the assigned debt collectors have the legal right to pursue and chase recovery of this debt for a period of Six years from the date of the last payment or acknowledgement.
After this period expires; the debt would become statute barred under the limitations act, unless they successfully obtain a CCJ within this said Six year period.
You could find it raises it's ugly head at any unexpected time to haunt you, on the other hand if you don't hear anything by it's Sixth anniversary you could consider it irrecoverable, hence treat it as such under the Six year rule, unless a CCJ is applied for in the meantime.