A lease granted in consideration for the tenant erecting a building or carrying out works to existing buildings is sometimes called a ‘building lease’. When a building lease falls within the scope of section 19(1)(b) of the Landlord and Tenant Act 1927 (LTA 1927), in certain circumstances, statute intervenes to override the express contractual alienation provisions in the lease. This Practice Note looks at the scope and effect of LTA 1927, s 19(1)(b). For general guidance on assignment and underletting, see: Assignment and underletting—overview. Building leases within LTA 1927, s 19(1)(b) LTA 1927, s 19(1)(b) applies to leases granted: • for a term of more than 40 years • in consideration wholly or partially of the erection, or the substantial improvement, addition or alteration of buildings • where the landlord is not a government department, a local or public authority, or a statutory or public utility company, and • the lease is not of an agricultural holding, a farm business tenancy or a mining lease It does not apply to occupation contracts within the meaning of section