There is no common-law requirement for the landlord to have served a rent demand on the tenant before commencing proceedings if those proceedings only claim payment of the sums due: Van Haarlam v Kasnar  36 EG 135.
Most commercial leases are protected under Part II Landlord and Tenant Act 1954 and so the requirement under Landlord and Tenant Act 1987, ss. 47 and 48 requiring the landlord to give notice and put their name and address on all rent demands do not apply.
Landlords should, however, be mindful of any costs implications in initiating proceedings without abiding by the spirit of the Civil Procedure Rules and without having properly notified the tenant of their intention to do with a letter before action.
If the landlord intends to pursue former tenants or guarantors for rent arrears a notice under the Landlord and Tenant (Covenants) Act 1995, s.17 must be served.