Here we have the usual "lets misuse British Standards for sales purposes" as often used.
The standard is an installation standard for new systems and is not retrospective or every system before 2002 (or even 2008) would have to be immediately ripped out.
I totally agree that any NEW installation should comply with BS5839-1 2002+A2:2008 and have identical types/makes of call points.
But not existing systems. I hate with a vengeance the use of a BS to spread, well...BS!
I understand that the fire protection companies need to try & flog as much kit as possible as part of their business and can see why, although not forgiveable, people use & abuse BSI and other guides to their advantage.
I'm employed not to sell call points, fire doorsets, etc and will instead look at a building & make sure that life safety is adequate, legal compliance is met and expenditure to achieve this reasonable and where necessary. This often refers to British Standards, but does not slavishly insist everywhere constantly rips out stuff to ensure it meets this months amendment of BS 12345678.
So back to a scenario influenced by the original post:
Seeing as all the call points are red, they all have the appropriate pictographic safety sign above, al say 'Fire - Break Glass', they all require the breaking of a frangible element to operate, and if required have hammers, does it reduce life safety to a standard below that required by the Fire Safety Order if one is the latest KAC type, 3 the older World Series, and the remaining 25 Gents circa 1970's?
Answer - No!
British Standards are not law, often are not retrospective (or only in part) and in many cases can be easily by passed in part to a degree that would still be defensible in court.
It happens with extinguishers - a lock up single room shop with one entrance the size of my through lounge/diner requires at least two 13A rated extinguishers or one massive powder or water/foam with additive rated 27A if you quote BS* and some extinguisher firms exploit this (& chuck in a Co2 with each the two waters they have just flogged - ker-ching!) despite a 13A 2 kilo Powder or even a 1 kilo 8A Powder actually being more realistic.
* from section 6.2- "Where, as a result of a risk assessment, it is determined portable fire-fighting equipment should be installed, the lowest level of provision likely to provide a realistic level of protection can be calculated by the total class A rating of all extinguishers on that storey. This should be not less than 0.065 3 floor area of storey (in m2) and should not be less than 26A"