In any case where—
relevant costs are incurred or to be incurred on the carrying out of works which are included in the external works specified in a group repair scheme, within the meaning of Part I of the Housing Grants, Construction and Regeneration Act 1996, and
the landlord participated or is participating in that scheme as an assisted participant,
the amount which, in relation to the landlord, is the balance of the cost determined in accordance with section 69(3) of the Housing Grants, Construction and Regeneration Act 1996 shall be deducted from the costs, and the amount of the service charge payable shall be reduced accordingly.