law: 6. Lawful increases of standard rent.-
  (1) Where a landlord has at any time, whether before or after the commencement of this Act, incurred expenditure for any improvement, addition or structural
  alteration in the premises , not being expenditure on decoration or tenantable repairs necessary or usual for such premises, and the cost of that improvement, addition or alteration has not been taken into account in determining the standard rent of the premises, the landlord may lawfully increase the standard rent per year by an amount not exceeding seven and a half per cent. of such cost.
  (2) Where a landlord pays in respect of the premises any charge for electricity or water consumed in the premises or any other charge levied by a local authority having jurisdiction in the area which is ordinarily payable by the tenant, he may recover from the tenant any amount so paid by him; but no landlord shall recover from the tenant whether by means of an increase in rent or otherwise the amount of any tax on building or land imposed in respect of the premises occupied by the tenant: Provided that nothing in this sub-section shall affect the liability of any tenant under an agreement entered into before the 1st day of January, 1952, whether express or implied, to pay from time to time the amount of any such tax as aforesaid.
  (3) Where a part of the premises let for use to a tenant has been sub-let by him-
  (a) the landlord may lawfully increase the rent payable by the tenant-
  (i) in the case of any premises let for residential purposes, by an amount not exceeding twelve and one-half per cent. of the standard rent of the part sub-let;
  (ii) in the case of any premises let for other purposes, by an amount not exceeding twenty-five per cent. of the standard rent of the part sub-let;
  (b) the tenant may lawfully increase the rent payable by the sub-tenant-
  (i) in the case of any premises let for residential purposes, by an amount not exceeding twenty-five per cent. of the standard rent of the part sub-let; and
  (ii) in the case of any premises let for other purposes, by an amount not exceeding fifty per cent. of the standard rent of the part sub-let;
  (c) the tenant shall, on being so requested in writing by the landlord, supply, within fourteen days of such request being made, a statement in writing giving full particulars of any sub-letting including the rent charged.