In a workplace the employer, or whoever otherwise controls the premises, is the responsible person and simply pays for assessing the areas they control. Multi-let commercial buildings split the job: each occupier assesses its own demise, the landlord assesses the common parts, and the landlord's share normally comes back through the commercial service charge. Under a full repairing and insuring lease, compliance costs for the demised space sit squarely with the tenant.
Where a site has several responsible persons they must cooperate and share information, a duty sharpened by Section 156 of the Building Safety Act 2022, so the sensible arrangement is to agree in writing who commissions what before anyone books an assessor. Mixed-use buildings are the classic case: residential common parts, commercial units and shared plant can each sit with a different payer, and the gaps between them are where enforcement finds nobody in charge. Identifying the duty holder first, as who is the responsible person in a fire risk assessment sets out, settles most payment arguments before they start.