Tom,
Dead Right BSs are confusing but I noticed you mention 5266-1 1999, which was superseded by the 2005 edition.
Don't know if this helps but the scope of the 2005 says
The 1999 edition of this standard no longer covered the levels of illumination
required as these are dealt with in BS EN 1838:1999 (also numbered
BS 5266-7:1999). References to BS EN 1838:1999/BS 5266-7:1999 are made at
the relevant points in the text.
The standard has now been revised again to remove recommendations and
guidance on the characteristics of emergency lighting systems that are now
specified in BS EN 50172:2004 (also numbered BS 5266-8:2004). References to
BS EN 50172:2004/BS 5266-8:2004 are made at the relevant points in the text.
This part of BS 5266 has thus become a base document, which, in addition to
giving basic guidance on emergency lighting, provides a guide to navigation of the
other parts of the BS 5266 series.
This revision of BS 5266-1 is applicable to cinemas, and also to other premises
used for entertainment, some of which were excluded from the 1999 edition.
BS EN 50172:2004, 4.1 specifies compliance with the wiring rules given in
HD 384/HD 60364. The UK applicable parts of HD 384/HD 60364 are
implemented in the IEE Wiring Regulations (BS 7671).
This revision of BS 5266-1 incorporates changes necessitated by the publication
of BS EN 50172. It does not represent a full review or revision of the standard,
which will be undertaken in due course.