FRI stands for a Full Repairing and Insuring lease where the tenant has responsibility for all external and internal maintenance, decorations and repairs as well as the liability for insuring the building. Under an FRI lease the landlord has no repairing or insuring liability.
 
IRI stands for an Internal Repairing Insuring lease where the tenant will have a narrower liability for maintenance, decorations, repairs and insurance confined to the internal parts of the property occupied by him/her. In such cases it is wise to check that the landlord is liable for the repair and maintenance and insurance of the common parts and exterior of the building. In some cases the landlord may insure the whole of the building. The landlord’s costs, e.g. for insurance or maintenance may well be recoverable from the occupiers through a service charge and the arrangements will be contained in the lease. IRI leases are normally granted where buildings are in multiple occupation and tenants often have similar repairing liabilities etc for the part of the building occupied by them.
 
You are strongly advised to seek professional advice before committing yourself to any liability. Some repairing liabilities may result in the tenant having to repair existing defects.