The "Guide to Fire Precautions in Existing Places of Entertainment and Like Premises" ISBN: 0113409079 commonly called the yellow guide is currently out of print but the following website
http://www.firesafe.org.uk/html/guides/basicmoe.htmgives,
(note this refers to licensed premises and also there are other ways of looking at evacuation times)
Time of evacuation is dependent on on the following factors;
Building construction
Occupancy
The construction of buildings are divided into three basic types,
Class A - complete noncombustible construction, i.e. elements of structure, floors, and walls. Supporting structure of brick or concrete;
Class B - traditional construction, i.e. noncombustible walls with combustible floors;
Class C - combustible construction, i.e. timber floors and walls.
Based on these classes arbitrary evacuation times were decided upon and the times that are generally accepted as -;
Class 'A' construction - 3 minutes
Class 'B' construction - 2.5 minutes
Class 'C' construction - 2 minutes
These are not hard and fast times, and can be extended or reduced according to the particular circumstances