Can my employer refuse to pay old debts?

I have a 22 year old debt to the department for work and pensions, they contacted me 2 years ago for payment stating I had been over paid an amount of income support in 1991/92 of £1600.

After some legal advice I called told them it was statuary barred they agree!

Now they have just contacted me again 2 years later stating that under new regulations they have instructed my employer to do a direct earnings attachment (with out a court order) to deduct monies from my earnings.

Can my employer refuse this as it is such an old debt?