accommodation available to let. Local authorities in England and Wales were given power to prosecute in the magistrates' court. The Housing Repairs and Rents Act 1954 sought to encourage landlords to repair controlled houses by allowing a "repairs increase" in the rent for houses brought into. and maintained in, good repair. It also sought to encourage the building and conversion of houses for letting to tenants by excluding from control all dwelling-houses built after 30 August 1954 and all separate, self-contained dwellings produced by conversion after that date, except in cases that had attracted improvement grants. Rent tribunals were empowered to fix, upon application, an appropriate increase in the rent for increases in the cost of providing services in pre 1939 Act controlled tenancies. All tenancies owned by local authorities, development corporations and housing associations and trusts were excluded from the application of the Rent Acts. The passing on to the tenant of rates increases and limited increases in rent attributable to improvements or structural alterations carried out by the landlord to a dwelling had been permitted since the inception of the Rent Acts. The 1954 Act permitted specified increases for dwelling-houses that were kept in good repair by the landlord, but limited the total rent recoverable to twice the gross value of the dwelling-house. It removed the ban on premiums in the case of the assignment of leases granted for periods exceeding 21 years, it relaxed the rules if a premium was paid on the grant, continuance, renewal or assignment of a tenancy if it consisted of reasonable expenditure on alterations or improvements, or a reasonable amount for goodwill. Extension and release Part l of the Landlord and Tenant Act 1954 extended Rent Act protection to tenants under long leases at low rents, and to the sub-tenants of tenants under such leases, by providing a procedure that converted those tenants into statutory tenants on the expiry of their tenancies. The Requisitioned Houses and Housing (Amendment) Act 1955 released from requisition those houses where the licensed occupier was accepted by the owner as a statutory tenant. The owner of the house was compensated for giving up the right to possession. Passed only after several particularly severe smoke-polluted fogs (called "smog") in London and the industrial towns had caused health problems, the Clean Air Act 1956 (which applied north and south of the border) reimbursed expenditure spent on the adaptation of