From the Guidance Manual:
Deductions from social security benefits
3.572 If a deduction is being made from a social security benefit, take the amount into account at the rate before the deduction is made.
P3.573 But take the benefit into account at the rate after the adjustment is made, if an adjustment is being made from the social security benefit under
* the Social Security (Overlapping Benefits) Regulations 1979
* the Social Security (Hospital In-patients) Regulations 1975 (these refer to downrating of benefits of hospital in-patients)
* section 30DD or section 30E of the Social Security Contributions and Benefits Act 1992 (deductions in incapacity benefit in respect of pensions and councillor’s allowances)
“HB Reg 25(3) & (4) CTB Reg 17(3) & (4)”
I think it’s that last bullet point that you want