Just as a little background to kurnals comments, the published procedural guidance for Building Regulations and fire safety states:
"Although these Regulations requirements are applicable to a workplace building whilst in operation it would be useful for the designers of a building to carry out at least a preliminary fire risk assessment as part of the design process. The level of detail of this assessment will vary depending on the amount of information available to the designer and whether or not the eventual occupier of the building is known at the design stage.
1.21 If a preliminary risk assessment is produced it can be used as part of the Building Regulations submission and can assist the fire safety enforcing authority in providing advice at an early stage as to what, if any, additional provisions may be necessary when the building is first occupied. It will also assist employers the responsible person when developing the full fire risk assessment for the purposes of the Workplace Fire Regulations Fire Safety Order, and it will act as a record of the rationale behind the fire safety
design of the finished building."
This dates from 2007 and does not contradict the more detailed and accurate picture kurnal portrays of where we are today.
For some large buildings I have done a pre-opening FRA to try to make sure that the building is, at least, reasonably safe when it first opens; and then followed this, about a month after opening, with a final FRA that sees the fuller picture of the building plus how its occupants interact with it.
Stu