I think this is covered in BS 5839 Part 8 - 2008. Clause 40.1 sets ot a requirement for weekly testing. Refer to extract below:
40.1 On a weekly basis, the responsible person should ensure that:
a) the system is tested by operating a manual call point on the fire detection system and the correct emergency message is broadcast in the correct emergency loudspeaker zone according to the cause and effect plan;
NOTE It is not sufficient to test emergency messages from controls at the VACIE alone.
b) an emergency microphone and its associated controls is checked for correct operation including tests of emergency loudspeaker zones and emergency message controls as follows:
• for Type V2 systems, check that a live message is broadcast;
• for Type V3 and V4 systems, check that the live message is broadcast correctly in at least one zone;
• for Type V4 systems, check that the pre-recorded message is broadcast correctly in at least one zone.
The standard also describes tests being undertaken at approx the same time each week, with an instruction to occupants to respond to any poor intelligibility etc. It further recommends that pre test warning announcements and post test "stand downs" are also adopted
Regards
Owen