A Diminution Valuation is a specialist’s report prepared by an experienced Valuer which takes into account Section 18 of the Landlord and Tenant Act 1927. Section 18(1) provides that the damages for breach of the repairing covenant may not exceed the diminution in value of the landlord’s reversion caused by breaches of repair. The common law practice is now to produce a single diminution valuation reflecting all breaches of covenant (i.e. including reinstatement etc).