You usually need the landlord's consent to assign the lease. Typically, the landlord cannot 'unreasonably' withhold consent. He can impose conditions but these must be reasonable.
The key issue is usually the financial standing of the proposed new tenant. The landlord may well ask to see the proposed tenant's accounts, ask for references, and use a credit rating agency to check their creditworthiness. He may ask for a deposit and if the proposed new tenant is a limited company, the landlord may also ask for personal guarantees from the directors of the company.
